Here's what our battery specialist has to say:
As far as consumer-level test equipment, maybe check out the
Xtar VC2. I'm not sure how helpful it might be to you, but it allegedly
can tell you the actual mAh capacity of your battery. That info may help you determine when to replace the battery when damaged or old.
As a battery ages the mAh of the battery (capacity) degrades, as the mAh degrades so does the batteries c rating (amp limit). So down the road, your 20A battery may only be a 10A battery.
How to test your batteries mAh capacity with the VC2:
Step 1: Insert your discharged battery (at a discharge cut-off voltage generally below 3.0V)
Step 2: Let the battery charge and notice the 0000mAh displayed on the screen. Do not remove the battery until the charge is complete.
Step 3: When the battery is fully charged, the screen will show "FULL" and the entire screen will flash 3 times every 10 seconds.
Step 4:
The mAh on the screen should now give you the batteries actual capacity.