Jim wrote in
ink.net:

I'm upgrading my charger to a Xantrex "True Charge" 40 amp, 3 stage
charger. The "Equalizer" function is important to maintain the
batteries.



The batteries only need 20A, so that leaves you with 20A of load current
while the charger is on.

The battery store guy should know better. 220 ampere-hours has nothing
to do with 220 amps. Ampere-Hour is a measure of the stored energy in
the battery. The "rating" only holds true for ONE load, the load that
drains it in 20 hours (that's about standard in the battery biz). 11
amps will drain it in 20 hours, so that would be the "standard load" for
this battery. The slower you discharge it, the more ampere-hours of
energy it will produce, way beyond its rating. The FASTER you discharge
it, more than 11 amps, the LESS its ampere-hour capacity is at that load.
This is caused by chemistry and physics. The chemistry is the speed at
which the acid can eat away at the soft lead plate's surface area.
Quickly discharging it with a heavy load, the acid by the plate is
quickly consumed into lead sulphate ions in suspension, blocking more
acid from attacking the plate surface. So, it's not some incredible
limit. Starting batteries overcome this problem with an incredible
number of plates producing an incredible surface area that can produce an
incredible instantaneous current.....but for a price. To keep the
physical battery size, the plates have to be very thin. Their amp-hour
rating is actually very low, as anyone who has been cranking a dead motor
for a few minutes when the lights go out can attest. Deep discharge
batteries use thick plates with lots of lead to eat and much more acid to
eat them....at a slower rate, 20 hours standard. At 50A, and I'm only
guessing as I don't have a chart in front of me but you can find them on
the net, the AH rating of the 220 AH battery is probably about half,
maybe a little more. Well, you get the picture. It's not a bottomless
pit of power, actually kind of small for its weight.

Nice charger, but you'll only see 40A charging them for a few minutes
before the charge quickly tapers off to a safe charging level below 20A.
If you never discharge them below specific gravity of 1.125, they'll last
a long time.