is there a way to fix a battery that is starting to stop holding a charge?
Yes there is. Buy or borrow a battery reconditioner. These can make the battery hold a charge better by charging and cycling them. The good ones will even evaluate the performance of the battery too.
On a related but slightly different note, does anyone have data or information on passive battery drain? When we charge batteries, then let them sit for a week or more, they don’t seem to perform as well as freshly charged batteries.
The best combination for batteries seems to be
-recently purchased
-fully drained
-recently charged
I wish we could let our drained batteries sit until 2 hours before each use, but we can never remember to charge them that way, so we usually charge as soon as they are discharged, which isn’t ideal. Does anyone have a better system?
NiCD and NiMH (and pretty much any battery for that matter) will have a self discharge rate. There are some special NiCD and NiMH batteries that have low self discharge, but they are usually lower capacity and of course they aren’t Vex legal.
A good battery charger will do a normal charge on a battery and then switch to a trickle, this will keep it nice and topped off.
I don’t know about the Vex batteries, but I would suspect that a week after charging they’d have lost some power. A month and I bet they’d be almost flat.
It doesn’t hurt to top off a battery, so if your battery is a week old from charging, just throw it back on for a little while.
You might consider investing in a good battery charger / discharger, though I guess the Vex one is the one you have to use for competitions. But having a single good charger would at least let you weed out any really terrible batteries (they do eventually stop working very well) and find the jewels of your battery supply.
I have an MRC Super Brain 977 (stupid name, I know) and it has 2 ports for batteries. Both can charge and one of them can discharge. It can charge and discharge at a huge variety of rates and will tell you how many mah it puts in (not a good way to determine capacity) as well as how many it can pull out (the way to determine capacity).
It is all manually set (including the peak charge detection), but uses some sane defaults. It has a great manual that explains all the various aspects of batteries (it’ll charge Pb, NiCD, NiMH and LiPO).
I use it to charge my 9.6v packs for transmitters, 7.2v packs that are kind of old and a pair of 8.4v packs that are brand new that I love 