The digital charger that I bought has a charge percentage of the battery and a voltage. Both batteries charged up to 64% within an hour or so. But it took the last 6 hours to get them to 67%. Any idea on what could cause this?
I'll give you some math
Each cell in the battery charges to 2.1-2.3 volts So a fully charged battery is some where between 12.5 to 13 volts All electrical equipment has a +/- 10% tolerance built into it If it is designed to run on 10v it is designed to run without any loss of preforming between 9-11 v It might make a little heat dew to resistants
so if 12.5 V. is charged Your battery is somewhere between 8-9??? v. now But that does not tell you the state of the batterys capacitances (I think that is the right word It has been 25 years since i got out of collage For H,V,A/C )