Do you have to charge the agm batteries or does it run off the alternator?

The alternator, AGM are not like NiMH, NiCAD, or Lithium Batteries that require special chargers to charge them.

Edited April 19, 201213 yr by Skullz

but once fully charged they can be installed and charged off the alternator.

Actually AGM does require a special charger. Hence the reason the make and AGM setting on most nowadays. They should not be charged any higher the 2.4vpc or 14.7v max. Anything higher 15v+ you risk damage to the battery.

Alternators are not meant as battery chargers only maintainers. It is a good practice to charge your batteries ~1 a month if you take short trips(15-20 min) along with heavy listening of the system.

3-STEP CHARGE PROFILE

INPUT

– 120V, 60 Hz, single phase; current varies with model

OUTPUT

– Three-Step charge profile (see figure below)

Bulk Phase

– Fast charges the battery up to 14.7V and gets the battery to about 80% state

of charge

Absorption Phase

– Finishes off the charge in no more than an additional 4 to 6 hours after completion of bulk charge

Float Charge

– Continuous trickle charge will keep the battery topped off

and ready to go

i think his question was more simple tho......

i think he was asking... when adding a battery in the trunk.. do you hook it up to your cars charging system.. or do you have to charge with a battery charger periodically

i believe hes a beginner that does not fully understand how to add a second cell

running an AGM battery off of the cars alternator will charge it. Every once in a while you might want to throw a changer on it to top them off and keep them in the best shape they can be.