Ian Malcolm wrote:
Phil Allison


** The cells in a particular battery have a great deal in common - eg
same origin, age, capacity, number and level of charges and
discharges.

Various 12 batteries likely have none of the above in common so
charging in series will not suit more a than one of them.

In the OP's case, with all new and unused batteries of the same type,
parallel charging with a fixed maximum voltage of 13.8 is the most
practical method as one can use a standard charger.

Each battery will initially draw the current it needs until all are
fully charged, then the current will taper off to a trickle in each.

Gel and SLA cells behave very differently to NiCd and NiMh cells.

*EXACTLY*
The charger should be rated for the maximum total AH capacity to be
connected to it and needs to be set for SLA batterys and to have a
constant float mode.

** Most Gel/SLA chargers have affixed maximum voltage between 13.8 and 14 volts which IS the float mode. A fully charged 6 cell battery will draw only a trickle of current at this voltage.

They also normally have a "current limit" feature that operates when a partly or fully discharged battery is connected, which ought not apply in the OP's case.


A 12V 10W bulb in series with each battery will prevent excessive current
flow allowing discharged batteries to be recharged safely and also
provides visual indication of any shorts.


** With bulbs like that fitted, a SLA charger rated at say 3 or 4 amps would do fine with 6 x 7AH batteries at once in the OP's situation.



..... Phil