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Old 07-21-2017, 03:05 AM   #12
Chance
Senior Member
 
Brand: Still Looking
State: Texas
Posts: 6,187
THOR #2121
Quote:
Originally Posted by Tfryman View Post
What you are saying is correct except for one thing: "Internal Resistance" really has no bearing on charge rate. Sure, internal resistance does impede both charging and discharging current and creates heat in the battery, but what determines the amps going into a battery is the difference between the source voltage (the charger) and the battery voltage. When the battery voltage increases, charging current will decrease. When charging batteries in parallel, as long as they have the same chemistry they will all have the same "full" battery voltage. Some of the batteries may reach that voltage before others, even if they all are the same make/model/AH/age. The ones that reach that voltage first will have almost no current applied to them, the lower voltage batteries will be receiving the charging current. When the charging circuit senses charging current to all batteries has decreased to its pre-set value, it will kick the charging voltage down to the "maintaining" voltage; normally about 13 volts.
Perhaps semantics, but if you have two batteries with different internal resistance such that one gets more current than the other, doesn't that mean faster charging -- everything else like charge voltage being the same?

An argument can be made that the battery with less resistance gets slightly higher current and therefore charges slightly faster. And if charging is interrupted prior to both batteries reaching 100% state of charge (say one at 70% and other at 60% as an example) then the two "should" equalize to a common voltage. Some "experts" claim this is inefficient, but I'm not sure it would be a deal breaker for me.

I would not discard a good battery (or two) just because it's a little different, unless they are so small that they don't contribute much anyway. That's why I'd confirm the capacity of the Dekas. Something doesn't seem right with the 75 A-hour rating.
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