Definately something wrong going on here. 4.59v and 4.65v is WAY, WAY to high (dangerous!). No way I would trust the batteries or the charger after reading what you just posted. I’m with scaru on the idea of pitching both of the batteries and the charger. I will suggest *one more time *for you to just switch to cr123a batteries for safety’s sake. At least until you get a handle on how Lithium batteries are used and charged. There is a learning curve and each different chemistry requires slightly different charging procedures. Your light does support cr123a batteries and they are safe. Use them up like you would use a alkaline battery and throw them away. Going camping? Take a bunch of spare batteries (cr123a) with you. No need for a charger because you can’t recharge them. Buy bulk. They have a shelf life of about 10 years. Enjoy your light and be safe. You can always switch back to rechargable batteries after you learn how to use them and what to expect from them.
Yep, I second what yellowhorse said. Hang around here for a few months and learn about lion batteries then you can make and informed decision on whether or not you want to use them.
You could also swap the driver in the manafont drop in to one that has low voltage protection. It will flash st 3.8 volts kick down to low at 3.7 volts and shut off at 3.6 volts. that way you don’t ruin anymore batteries.
What drop-in can do that?
Wow! My last post was ugly. No idea what happened. I did not “bold” anything. Hmmmm.
Again Thanks!
Scaru you are “scaruing” te heck out of me!.
Now very seriously, I got the point with the hazard issue (this is really getting scary and complicated). I will check the CR123 batteries as suggested and use the flash with those.
E, Do you know the part number for that protected driver. If not, I will try asking the Manafont people they seem to be very helpful.
These is getting out of topic but for future reference How you avoid overcharging batteries? Isn’t that something that the charger is supposed to do after it turn the leds from red to green? Does it keep putting more charge on the batteries? So what you do? Charge them for half an hour take measurements charge another period of time take measurements again and keep doing that until you get 4.2v? I will check if this particular model of charger is suppose to do that, it could be that it is factory damage and in that case ask Manafont.
Again many many thanks. And again I got the point loud and clear with the hazard and all that so don’t sweat.
In order to prevent over charging you need to get a better battery charger and better batteries. 
It also is a good idea to monitor the batteries while they are charging and periodically check the voltage. I hope I didn’t scare you to much but I find the best way to keep someone safe is to scare them and then let them learn it over time.
And don’t feel dumb about this. This is probably a million times safer than the guy who was charging one using a car battery, wire, and a piece of pencil lead. Sorry about the bad spacing my iPhone hated this post editor. 
Oh not at all, let me say it, I’m an ignorant, but after today a bit less. Good thing is to learn, but even better is to learn avoiding melting your eyes, nose, throat, esophagus and lungs as you put it. 
Good way to think about it. Also if you want to continue using rechargeables but without the danger of normal lions you can get lifepo4 batteries. The advantage to these is you don’t have to worry as much about voltage as these are much less likely to vent with flames. The disadvantage is they have a lower capacity and voltage, they also require a less common type of charger.
Maybe his DMM is weird too?
Isnt that a little early? 3.6V under load is like.. 1/3 of the capacity @ 3A.
I would check your DMM too.
My first thought was also the DMM. No ways the li-ion reaches 4.6V without even any warning signs, and there's two of them even.
At least do some jiggling first on the DMM - wire leads, knob, power switch - all of them. Sometimes DMMs just do these things.
My bet is that you just over-discharged the batteries a bit at first. The charger refused to charge. You let the batteries rest, the voltage goes up, then the charger allows charging. THEN your DMM decided to play a joke on you. 
Just try to get second readings first before throwing everything away.
Simple the batteries should charge in that charger to about 4.21violts ..just a tiny bit over 4.2 volts that is pretty common for these chargers if it doesn't than there is some sort of problem .The charger has a red light when you put batteries in and green when they are done charging and should be charged in a safe place and with you present ..Not just left on a charger overnight . Ther are always many ways to skin a cat .. you could charge them ina fireproof box that is vented to fresh air and not in the house ..or in a fireplace on a timer ?? in the garage agin in a fire proof box or a metal bucket .. i don't think lithium ion is all that dangerous but if i got real numbers like you just said ...my gear wouldn't be in my office ..it would be on concrete in a metal box on the covered yet fresh air vented back porch . i'd check the meter first and see if you get a 4,65?? reading from a second meter if so i'd say the batteries and charger need replaced i'd call wjhomever i just bought them from ..manafont or dx or whoever and be getting a replacemnet sent ..i've recommended this charger to lots of people but wouldn't stake my life on it and I didn't manufacture it so i wouldn't put my reputation on it either but it's a commonly used charger so osme thing is definately wrong ...I 'd like to think it's a bad meter reading that would make everyone feel better ..4,6 on one battery is insane .. on two is really really crazy .
Check the numbers on another meter asap and hopefully you just have a junk meter
as far as when to change batteries it's simple .. when you notice that the light is getting dim just swap batteries . lots of times it won't have enough juice to do high mode any longer it will only do med or low then it's obvious it's time to change batteries .
you don't need an electrical degree to figure out lithium batteries you simply need to read thru some basic warings and just respect them same as you would a knife or certain chemicals.
the 18650 would have probably been a better choice since it has MUCH more power and there are some really good ones since so much reasearch has been done on them for power tools and laptop computers ..for a bike you might want to grab a solarforce host like the L2m for 11$ and a few( good 18650's)..really bright lights need the juice and they need batteries that can deliver ..one of your best investments is in good batteries (japanese) panasonics /sanyo
Thanks for your suggestions. I will keep this flashlight but I’m looking for a new one.