Charging a deep cycle battery

If you have 2 batteries on your boat, 1 deep cycle and 1 cranking, do you charge the deep cycle as you would the cranking. In other words does charging the deep cycle using the alternator from the boat charge it the correct way. Or do you only charge the deep cycle on a battery charger in the deep cycle mode.

Re: Charging a deep cycle battery

So the correct answer is 'it depends....' What kind of boat, and how discharged is the deep cycle?


If you have a real alternator, and the deep cycle isn't completely dead, a properly set up dual battery system will be fine.

If you have an outboard and a 100% dead deep cycle, not a chance!

Re: Charging a deep cycle battery

My understanding is that it is best to deeply drain it, and use a smart charger to refresh it.

There are some batteries that can be trained to have a shallow charge, and this can happen with a deep cycle battery when you drain it a little and charge it a little. You tend to rob it of its deep cycle capability.

Deep draining and charging up with a smart charger -- not some basic/manual charger. Your alternator is the latter.

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Re: Charging a deep cycle battery

Philster said:

My understanding is that it is best to deeply drain it, and use a smart charger to refresh it.

There are some batteries that can be trained to have a shallow charge, and this can happen with a deep cycle battery when you drain it a little and charge it a little. You tend to rob it of its deep cycle capability.

Click to expand...

Nope... Deeply discharging deep cycles also hurts their capacity. A deep cycle isn't that much different than a starting battery, the plates are just constructed slightly differently. The reason it is a deep cycle is that it can tolerate low discharge better than a starting battery, at the expense of cranking amps. With either design, deep discharging it will still cause degradation of the plates. Lead acid batteries do not have any memory affect, cycling them is pointless and damaging.

http://www.batteriesinaflash.com/deep-cycle-battery-faq

"The lifetime of a battery is directly related to the depth of the discharge that it regularly experiences. Lead acid batteries are fickle things. If you subject a deep cycle battery to 80% DOD on a regular basis you will get roughly half the life out of your battery than if you were to cycle it to 50% DOD."

Re: Charging a deep cycle battery

Philster said:

My understanding is that it is best to deeply drain it, and use a smart charger to refresh it.

There are some batteries that can be trained to have a shallow charge, and this can happen with a deep cycle battery when you drain it a little and charge it a little. You tend to rob it of its deep cycle capability.

Deep draining and charging up with a smart charger -- not some basic/manual charger. Your alternator is the latter.

.

Click to expand...

Incorrect info.

The more you deep drain a lead acid battery, wether its a deep cycle or not, you are reducing its capacity. A deep cycle battery can tolerate deeper discharges than a starter type battery but still should never be discharged beyond 50% discharge.

Lead acid batteries do not have develop a memory like a Ni-Cad.

The alternator will charge the batteries because its not on over a long length of time and the charge current does taper. Still nice to have a smart charger when in storage becuase you want the battery to be fully charged so that it doesn't sulfate.

edit:I see smokingcrater types faster than me.

Re: Charging a deep cycle battery

This has always been a highly debated subject but maybe I can shed a little light on it. A true deep cycle battery has several rating numbers but when it comes to charging it's the number of cycles it can withstand. Just like a cell phone or computer battery the deep cycle battery charge cycle is counted as each time it is charged. Lead Acid battery's are a little more forgiving in that a short top off charge doesn't count as heavily against the max charge cycles as other battery types.

At 40% charge a deep cycle is considered discharged and should not be discharged any further. If you plan to get the maximum run time and the maximum charge cycles, this would be where you would want your battery to be everytime you put it on the charger. Bringing it back to a full charge is what you want to do and the alternator on your boat is rarely going to be running long enough to do that. However, the length of time it is charging is going to cost you one charge cycle.

What you are seeing more of today are combination start/deep cycle batteries. The RCA ratings on these batteries are often far less than a same size deep cycle but the charge cycles are much higher. These types of batteries are better suited for all but those of us that use our deep cycles for trolling motors or high output stereo systems, etc.

Given that info, you can see that your expensive true deep cycles need to be charged separately and when at 40% charge if possible.

Hope that helps.