How long to charge 12v deep cycle battery?

Question

How long would it take to charge this deep cycle battery (Amazon link) with a regular household electricity plug?

Thanks.

Answer 1

Recharging details for lead-acid batteries are detailed in many places (for example).

Quoting the linked site:

Recharge time can be approximated by dividing the amp hours to be
replaced by 90% of the rated output of the charger. For example, a 100 
amp hour battery with a 10 % discharge would need 10 amps replaced. 
Using a 5 amp charger, we have 10 amp hours divided by 90% of 5 amps 
(.9x5) amps = 2.22 hour recharge time estimate.  A deeply discharged 
battery deviates from this formula, requiring more time per amp to be 
replaced.

Applying this to your example, the linked battery is marked as 35Ah. If the battery is 50% discharged (you certainly wouldn't want to discharge a deep cycle/marine lead-acid battery further than this with any regularity if you care about its useful lifespan) then you have 17.5Ah to replace. If you have a 2 amp charger (not too uncommon), divide 17.5Ah by 90% of 2 to arrive at 9.7 hours.

This is only a rough estimate, of course (and as warned, the deeper the discharge, the less accurate the estimate; real charging time will likely be longer).

You could reasonably increase the size of the charger used on this battery to 25% of 35Ah - around 8 amps. However, my personal experience suggests that you won't actually get a much faster complete charge at 8 amps than you will at 2 amps. With an 8 amp charger, the voltage will rise much more quickly but this will largely reflect a surface charge which dissipates quickly on use.

You may also find it more effective to use a smarter charger which can apply a bulk charge phase, followed by an absorb charge phase, followed by a float charge phase. The different characteristics of these phases (with high amperage during bulk charging and long duration during absorb charging) produces the fastest complete charge. The above formulate doesn't purport to estimate how long it would take using such a charger but my personal experience suggests it would probably be around ... 10 to 12 hours.

Why does it take around the same amount of time to charge at 2 amps and at 8 amps? Because the 8 amp charge is wasting a lot of power as heat.

Answer 2

Jean-Paul's answer is part of the story. Charging rate influences the life of the battery.

• High power rate batteries (car starters) maximize the plate surface. They are designed to deliver a lot of current for a short period of time. They can be charged faster too, but suffer on deep discharge.

• Deep discharge batteries supply less current for a much longer period of time, and tolerate being run down much further. But they shouldn't be charged as fast.

The best way to charge a battery IMHO is with a smart trickle charger. These typically cost about 30-50 bucks, and will charge at 2 A peak. They also monitor the battery voltage, and will shut off when the voltage gets to a certain point, and restart after it drops a certain amount. It can take several days to charge a flat battery.

Your best bet is to to the maker's web site, and see what they recommend for charging rates.

When you get to battery systems -- say off grid use for a house, then you use smarter charging systems. Microprocessor controlled; a memory of the history of the charging, charge leveling to get the charge in each battery the same, voltage monitoring so that failing batteries can be spotted early. Battery controllers have a significant cost relative to the batteries.

Answer 3

Your battery is a lead acid one. Based on battery university guidance (link below), and assuming you are using a 'standard charger' should take 12 - 16 hours.

Battery University