Hi all: Apologies if I’ve not found a topic addressing this. I find myself looking for an upgrade battery / batteries for an old Makita cordless drill (Makita drill model # 6095D ). Wife loaned out my more modern cordless tools months ago. Needing a cordless drill, I dug out this old dinosaur and found the ancient batteries would not hold a charge for long at all; as in, scarcely getting one hole drilled in soft material. So I’m looking for as sound of a battery education, at least as sound as the lighting education that I certainly and gratefully got here at BLF. Thanks in advance for sound recommendations…
We're very glad to have you here, d_house!
SecondLifeStorage is the one.
There’s also Endless Sphere.
Also check out Battery University: https://batteryuniversity.com
Amazon has two 9.6v aftermarket battery packs for $20-25
Anything in particular that you want to know about those or other power tool batteries? NiCd or NiMH in general? The original NiCd were never that great and the later NiMH substitutes lasted a bit longer but could also die untimely deaths when people ran them down to zero and then kept trying to go further. Not sure what all is out there at this point but if you buy one of the packs be sure they will actually work with your original Makita charger (many will not, unless they all addressed that issue)…else buy the charger, too. Honestly I would consider looking at a cheapie li-ion drill kit instead, even a store brand or import weird-name brand as a backup rather than spending money on that ol’ fellow…nostalgic as they are. 
If your drill is a classic one and you want to keep it going much the same as you would an old car, fine. However you will find that since cordless technology is much newer than corded technology, you will find the new equipment is much better than the old equipment, Not to mention, cheaper.
If you do want to swap out your cells, there are too many videos on YouTube. Generally speaking, you will have to crack open the case (which most of the time permanently damages it.) Then you will have to solder the new batteries onto the BMS system and glue everything back together again.
Again, it can be done but unless you are a super careful, it will be a complete mess that will likely not work well or not work at all.
BTW, the: 6095D was my first drill purchased in the mid 80’s. Incredibly modern for its time but unfortunately a door stop by today’s standards. My opinion of course.
Alternatively, you can find cheap Chinese replacements as mentioned above. I have thrown too much money away on Chinese replacement batteries. They are sold with a new shell so they look shiny new and the cells inside are complete crap.
Having googled the model number, the battery pack looks like it might be challenging to open and replace the cells. If you’ve nothing to lose then might be worth a go opening the casing and seeing what’s inside (I would imagine sub-c NiCd cells).
If you end up replacing the cells, remember that cadmium in the cells is toxic so must be correctly disposed of.
Browsing the GJ site this weekend I saw a post mentioning this rebuild outfit here in the US. They’ve been around a long time and are apparently well respected. Have to send your old battery to them, they’ll replace the cells and send it back to you. Sounds like they reuse your contacts and board unless they can’t. The 9.6v product page: 9000 Makita® 9.6V Battery Rebuild Service – MTO Battery