Testing of Battery packs and modules.
OHM METERS FOR BATTERIES & CELLS
A lot of EVers want to find and need to find a quick and easy way of finding which ones of the cells and or modules are bad in their battery packs. HP makes a very expensive impedence tester for batteries; and like most people, it's not in my budget. I have been using for the past 5 or 10 years a Schumacher battery tester and it gets me very close into the ball park on which of traction batteries are going south. The only problem with it is it gives me the reading in CCA, of which there is a direct correlation to a Ohmic value. I have a small collection of 38 AH batteries that have been occasionally used for 12 & 24 volt applications, and they have not been charged as often as the ones in my XM 3000. One of my 12 volt batteries exploded and I had to replace it in order to have a 60 volt system and didn't want to put in a new (NIB) battery for it would quickly match the other weak or nearly-dead batteries that are in the scooter. I recently puchased an ugly-looking ohm meter on eBay for approx. $40.00 and was pleasantly surprised by its accuracy compared to HP meter.
When I recently tested my old supply of green batteries, they all had different ohmic values because I cycled them individually vs. being in a 60 volt application. I picked one with the same weight within an ounce of two and the same ohmic value as what was in my XM 3000 and installed it in my scooter. I marked it with an X as the latest replacement battery, charged the scooter pack until the green light came on, and rode the bike for 10 or 12 miles and recharged. I re-measured the individual 12 volt batteries and the impedence of all the batteries were almost all equal. I think that proves that charging and discharging a pack on a Pb-acid pack seems to self-balance the batteries. I have a 102 cells in my Vectrix with some 8 cell modules and 9 cell modules. I have of 9 cell modules I use for ham radio and computer applications. They are really my spares for my VX 1. I don't know if there is a BMS system in the Ni-MH battery pack. I do know if you install a Lithium pack, you need a BMS.
I went to Batteries Plus, and they wouldn't tell me too much about their battery testing procedures. I know from dealing with Interstate Battery that they have a sufficient amount of test equipment including ohm meters for batteries and load testers, and are a lot more knowledgable about batteries and their replacement. The price is so perfect for my budget that I'm going to get a couple more ohm meters from eBay to have and keep in my toolboxes. This eBay item is 60 bucks and I am going to get it and compare also.
One good thing about testing the impedance of cells, modules, and 12 volt battery packs is that you don't need to charge the cells in order to get a reading. Cycling the cells or modules might change the impedance a bit but it is basically the same discharged or charged a bit. If they vary a few milli-ohms and they are cycled in series they seem to self balance for Pb-acid pack. I am so impressed at this device. I can't figure out how I lived for so long without a Ohm meter for battery packs.