Review: New "Solarstorm" 2S2P 8.4V "water resistant" 4 x 18650 battery case for bicycle lights

Finaly manufacturer of an old 2S2P battery case made a new improved one. The old one has virtualy gone out of stock at any known seller. I've got cases from two sources (Gearbest and Kaidomain) to see if there is any variance in the production. The case is mostly used to power bicycle lights with 4 Li-ion 18650 cells of your choice. Cells are set in a 2S2P configuration which gives double capacity and 8.4V or can be used in 2S1P configuration.

The information about it has been already published in the thread here but I would like to make it in one place since I've done some important measurments.

Pictures of the case:

Electrical description:

There is an arror in description under nr. 6 - it should write: "USB maximum current ...... 2000mA"

The cells has to be inserted differently than with old case. It is marked in the case but I would advise you should mark it also on the cover near the springs so you can check again when you are closing the case. The cover is rectangular so it can't be placed in wrong direction. Cells are placed diagonaly so the cover can be inserted in any of two directions.

In the bottom of the case there are two connectors to connect cells in series.

What I don't like is that the all four are not cross connected like in the old case. That way electricaly looks like we would have two 8.4V cells in parallel. If they would be cross connected we would have like one big cell same as almost all welded 2S2P battery packs. What I'm also missing is the connection from the bottom to the protection circuit in order to check the voltage of each cell in series.

Protection Circuit

Big improvement in this new case is the protection circuit. I've made few measurments on different features.

Overcharging cut off kicks in somewhere at 8.46V in both cases. So if the charger fails to stop charging protection circuit would cut it off. Big and the most important improvement over the old case. Next feature is overdischarge protection. There I've got mixed result depending on the case and the current. It was funny when running at low current ovedischarge protection kicked in quite late, to late for my opinion. I've got 4.60V at virtual no load (0.02A just light connected), but 5.05V at 2.4A load (regulated single XM-L driver). So the cut off would depend on the load and the light you are using. To me this is not that important as I've found 4 different 2 led lights starts dimming much before and you'll notice low voltage anyway. Underdischarge protection restores at 6.0V at both samples if the cells can regenerate to that extend.

There are three status lights which shows the status (ie. voltage) of the pack when you push on the On/Off switch near to them.

Frame source Gearbest Kaidomain
3 status leds 8.4V 8.4V
2 status leds 7.45V 7.60V
1 status led 6.95V 7.10V
1 status led flashing 6.45V 6.60V

So the difference is constant 0.15V - not that much and probably due to resistors tolerance on the PCB. Showing status leds takes the 0.5mA current out of the batteries.

Standby current

Or in another words self discharging. By description it should be 10 microA. No way near the truth or it is just a mistake in the description: micro instead of mili. I've got 8.6mA with the Gearbest sample and 8.5mA with the Kaidomain sample. This can be of concern if you are leaving the pack uncharged for longer period. If we take the lowest 18650 cells capacity of 2200mAh we would use nowadays (ie. 4400mAh for the pack) it woud get drained in a 4400/8.5 = 518h or 21 days. This is bad news so be aware and take the cells out of the box when not used or recharged for more than 3 weeks or with higher capacities for a month.

Latest test shows this parasitic drain stays active all the time even when the cells drain below overdischarge point. This is dissapointing to me. Yet I can recall the similar issue with Magicshine ALU pack with led display showing the status. They might clone their circuit, though :(

EDIT: Newer circuit version S112A1 has much smaller parasitic drain

USB Output

Some would find it usable and some not. For the ones who would like to connet GPS/Phone in paralell to the light this would be usable. For the others this might be just unneded appendix. Anyway I've measure output voltage and got it 5.02V. It could charged my phone so it delivers at least 1A.

Pros:

  • protection circuit with overcharge and overdischarge protection
  • showing the stage of the pack
  • smaller and lighter than before
  • wide strap to fasten it to the bicycle frame
  • USB output (for some people only)
  • interchangable battery cells
  • cells can be charged outside of the case - balancing possibilities

Cons:

  • no cross connections in the bottom of the case
  • no connection from the bottom to the PCB
  • only Solarstorm type of connector (compatible somewhat with Magicshine, though)
  • no or bad water resistance (would need bit thicker o-ring)
  • no watter tight cover for USB connector
  • high standby current of 8.5mA (edit: much less in a new circuit version)

Overall impression


It is nice case and unfortunately the only one of that type I know. This version is more usable than previos one and much more safe to use, just like welded battery packs we are mostly see in the bicycle light sets. To bad it doesn't have cross connections at the bottom and wire to the PCB. In this regard welded battery packs are still better. On the other hand you can charge cells individualy from time to time to get balanced, but you need additional individual (multibay) charger. To bad the case is not very water resistant. Using some silicone grease would help to solve that somewhat. Big issue that I see now is high standby current of 8.5mA. Be aware and take cells out of the case when not used for a longer period ie. more than 3-4 weeks. Edit: Still valid to take batteries out, but with newer circuit version it takes longer to drain the cells.

To test in the future:
Would need to test also short protection and overcurrent protection. Actualy I would leave short test as a last thing to do and I don't have any high current drain device prepared right now. Would need to think of something....

Max. USB current is also to be tested in the future.

EDIT:

Protection circuit pictures


Really nice test!

We do not see many of those around. But then not many new boxes are made.

Thank you for your thorough testing. It is a very good reference for future builds.

Thanks for the review ledoman. I'm not sure if I'm missing something but which lead does it charge through? I assume protected batteries fit no problem.

Does the indicator works with 2 cell config? Nice review here!

Thanks to all. As with every 2S2P or similar packs charging is done via 5.5x2.1mm connector by 8.4V Li-Ion charger. USB lead is just for the output.

Yes, the protected cells does fit, but very tight. I think there is no need to use protected cells since the whole pack has protection circuit. Shure it is additional protection but it adds 2x on the voltage drop too. There is some variance in the protection circuits in the cell so they act each bit differently. Next, undercharge protection would trip in one pair before the other which leads to unevenly discharged cells. Also in this case you have to take the cells out in order to reset the protection. Well it depends whic cell in the series it was.

Now I've think of what I've forgot to write. Undercharge protection resets at 6.0V. Will add to the review.

Thanks. Yes of course, it is merely just a voltage level indicator. As long there is closed circuit (ie. at least 2 cells in series) it will show status.

Nice review, thanks. Might get one for diy projects that need 5V/8,4V and one for the bike.

I wish there were some of the shelf 2S1P cell holders availible. That would save a good amount of weight as I consider using my recently ordered Yinding as a headlamp from time to time. I think fenix had some but they don’t seem to sell them seperate.

There is discussion over at MTBR about 2 cell battery holder somewhere at the end of the Battery thread. Take a look at there.

You can use this case with two cells, too. Of course it is not suitable to be put on the helmet. We might try to ask the manufacturer to make one, but the chanches are rather small as the majority would still choose 2S2P packs, me including. Don't want to have additional weight on the helmet. It might be ok on the road and on simple trails, but when you have bumpy one with drops etc.. the weight on the head multiplies for the moment.

I guess people are starting to get delivery, as mine came today. Haven’t messed with it yet, but looks nice.

Forgot to emphaize, but can be seen in the linked thread, there is Coupon: New2S2P at GB for it.

Added new measurments to the review:

Standby current

Or in another words self discharging. By description it should be 10 microA. No way near the truth or it is just a mistake in the description: micro instead of mili. I've got 8.6mA with the Gearbest sample and 8.5mA with the Kaidomain sample. This can be of concern if you are leaving the pack uncharged for longer period. If we take the lowest 18650 cells capacity of 2200mAh we would use nowadays (ie. 4400mAh for the pack) it woud get drained in a 4400/8.5 = 518h or 21 days. This is bad news so be aware and take the cells out of the box when not used or recharged for more than 3 weeks or with higher capacities for a month.

Latest test shows this parasitic drain stays active all the time even when the cells drain below overdischarge point. This is dissapointing to me. Yet I can recall the similar issue with Magicshine ALU pack with led display showing the status. They might clone their circuit, though :( I think.

so protected cells are highly recommended, in case you forget to take the batteries out of the box for months

Yes, if this is the case then protected cells should do the job. Unforunately using protected cells would cause additional voltage drop. So we get some + and some -

I’d have thought that “not slowly becoming a bomb if neglected” ought to be assumed as a design specification on all new hardware.
But no.

I guess applying the precautionary principle would be a violation of the basic “cheap, fast, and good, pick two” rule.

I guess we start back at the same point with every new technology.

Thanks for the info.I have just backed off tho top screw 7 to 8 turns to break the contact.It’s a momentary switch,so when I push down on it ,the 3 leds come on,but on releasing the switch,the leds turn off.The cells rattle so no good for day riding like that.BTW,where do you guys live that you can even think of leaving the battery pack on the bike without it “walking” :stuck_out_tongue:
For me,I will have to velcro strap the battery on the bike as well as the light on to its base on the bars.Tightening down the lid is just part of the routine.

It appears that FastTech also has the case available with at least one Solarstorm flashlight. This is based on at least one answered question and looking at one photo of the light with all items.

http://www.fasttech.com/products/1527803

This is the old case showing with SS XT40 light, not the one from this review.

Added the pictures of the PCB to the end of the review.

Thanks for the great review ledoman! Awaiting delivery of the two I ordered from GearBest.

-Garry

Using four matched freshly charged li-ions

When I push the button, all three lights light up.
Push it again, all three lights go out.

With a Charger Doctor plugged into the USB port, it shows the port is hot regardless of the state of the little button on top.
(Haven’t checked the coaxial power port yet)

Is that as expected? The button and lights are just to check the state of charge, not to switch the power?
(I think that’s right, it’s described elsewhere as a LED Battery Indicator, not a power switch)

I suppose that could explain the parasitic drain, having the outputs are powered.

PS, on the list of features on the actual box, mine (last line) says the USB maximum voltage is limited to 2000 MA.
Any guess what that means?

Unfortunately the power to the connectors are live all the time. The power button doesn’t actually function as a power button. Go figure.

The Ching-glish translation meant 2000mA CURRENT not voltage.