What Is the Charge Time For A Deep Cycle Battery? (3 Things You Need To Know)

UPDATED 20 JULY 2022

by Eric Bartlett

Deep cycle batteries are ideal for providing a low, steady voltage over a long period of time, which is great for powering trolling motors and other boat electronics.

But in order to get the best results from your deep cycle battery, it’s essential to make sure that you charge it correctly, which includes charging it at the right amp rate, and for the right amount of time.

In this article we’ll walk you through how long it takes to charge a deep cycle battery, and what you need to be aware of in order to do it correctly. 

How long does it take to charge a deep cycle battery?

Battery reserve capacity2 AMP Charger4 AMP Charger6 AMP Charger10 AMP Charger15 AMP Charger
80 RC17.5 hours8.5 hours6 hours3.5 hours2.5 hours
140 RC27 hours13.5 hours9 hours5.5 hours3.5 hours
160 RC30 hours15 hours10 hours6 hours4 hours
180 RC33 hours16.5 hours11 hours6.5 hours4.5 hours

The table above shows the average charging time for deep cycle batteries, depending on the number of amps provided by the charger, as well as the reserve capacity (RC) of the battery.

These charging time estimates are for batteries that are 50% discharged.

It’s important to note that the exact charging time of a battery can vary depending on a number of factors, including how much charge it has left, what its reserve capacity and amp hour capacity is, as well as on its age and state of maintenance.

So it’s quite possible that the time you’ll get for your own battery will vary somewhat from the estimates given above.

For example, if your battery is completely empty when you start recharging it, it will take longer to charge.

If you’re interested in taking advantage of the extended charge offered by lithium batteries, check out our article: what is the cheapest lithium marine battery?

How long does it take to charge a trolling motor battery?

The time it takes to charge a trolling motor battery depends on the amperage provided by the battery charger as shown below:

  • 5 amp charger: 10 to 12 hours
  • 10 amp charger: 5 to 6 hours
  • 15 amp charger: 3 to 5 hours

The hours given above are average estimates of the time it takes to charge a standard 55 amp hour (Ah) trolling motor battery.

The higher the amperage provided by the charger, the faster it can charge a trolling motor battery.

But keep in mind that the charging time also depends on the reserve capacity and total amp hour capacity of the battery, as well as how new and well maintained it is.

In other words, a battery with higher capacity will take longer to be fully charged, and if it is old or damaged, this will also increase the time needed to do this.

All of this results in a lower runtime for your trolling motor, so it’s well worth paying attention to getting it right.

How long does it take to charge a deep cycle battery at 10 amps?

The time it takes to charge a trolling motor battery at 10 amps depends on the amp hour capacity of the battery as shown below:

  • 35Ah: 3 to 5 hours
  • 55Ah: 5 to 6 hours
  • 100Ah: 10 to 12 hours
  • 120Ah: 12 to 14 hours

In other words, the higher the amp hour (Ah) capacity of your deep cycle battery, the longer it takes to charge it. 

But keep in mind that the length of time it takes for this  also depends on its level of discharge, as well as the age and quality of the battery.

So take the numbers above as a rough estimate when extrapolating to your own case.

If you’re thinking about using your battery for a fish finder, check out our article do you need a deep cycle battery for a fish finder?

What amp rate should you use for a deep cycle battery?

It’s best to use a charger that provides between 5 and 15 amps for a deep cycle battery, and this is exactly the range in which most deep cycle marine battery chargers come.

For example, the Minn Kota Precision Charger is available with either a 6, 10, or 15 amp output.

Is it better to charge a deep cycle battery slow or fast?

In general, the higher the amp output, the faster your battery will be charged. However,  it’s better not to go above 15 amps output, sinc deep cycle batteries are built for a slow discharge rate, and therefore only tolerate a relatively slow recharge rate. 

Finally, another consideration to keep in mind is that a slow 5 amp charger is cheaper than a fast 15 amp charger. So if you have a relatively small 35Ah or 55Ah battery, you may not need to spend the extra money for the more expensive one. 

How do you know when your deep cycle battery is fully charged?

Most deep cycle battery chargers have an indicator light that shows you when the battery is fully charged, and automatically stop when they reach this point.

But in case your charger doesn’t have this feature, try to estimate the length of time required to charge your battery based on the numbers provided in our table above, and disconnect it when you reach that time.

While you can also determine the state of charge of your battery by measuring its voltage, this is not really advised, since it’s a relatively complicated procedure.

You need to use a voltmeter for this, and have to wait at least 6 hours after disconnecting it before you do the measurement. 

When should you stop charging your deep cycle battery?

You should stop charging your deep cycle battery when the indicator light of your charger shows that it’s fully charged, or when it reaches the estimated amount of time required to reach this point (which you can calculate by referring to our table above).

In general, it’s okay to continue charging the battery for a few hours after it’s full, but you don’t want to go much longer beyond this to avoid damaging the battery. 

Can you overcharge a deep cycle battery?

Yes, you can overcharge a deep cycle battery, which causes overheating and grid corrosion, and in the long run leads to reduced battery life and poor performance.

In order to avoid this, it’s best to use an automatic deep cycle battery charger, that detects when the battery reaches its full charge, and then automatically stops at this point and switches to maintenance mode.

Automatic chargers not only avoid overcharging a deep cycle battery, but you can also use them to keep your battery continuously charged during the off season, even if you don’t use the battery for months.

This prevents the battery from running empty and staying empty for a long period of time, which reduces both its lifetime and performance. 

Do you need a special charger for deep cycle batteries?

Yes, you need a charger that’s specifically designed for deep cycle batteries, which provides a lower amp output than regular battery chargers.

The reason for this is that deep cycle batteries are built to provide a slow steady current over a long time period, and hence  also require a slow recharge rate in order to avoid damaging them. 

While you can in principle use a regular charger (such as one you would use for a car battery) for a deep cycle battery, this results in excessive heat production, corrosion of the internal grid, and deformation of the plates.

If done repeatedly, this will dramatically shorten the lifespan of your deep cycle battery. 

How often should you charge a deep cycle battery?

If used intensively, a deep cycle battery should be charged every day. However, if you use it infrequently, or only for a short period at a time, it’s fine to charge once or twice a week.

But even if you use it very infrequently, the minimum charging frequency should be once a month, to avoid it running empty for long periods of time, which will tend to damage the battery. 

If you’re an angler, you may be interested in our article: what are the best fish finder batteries?

Do you need to charge a new deep cycle battery?

A newly purchased deep cycle battery should be fully charged when you get it, but it doesn’t hurt to top it up before use.

\Also, keep in mind that when you start using a new deep cycle battery, it will take several cycles to reach its maximum capacity.

It helps to speed up this process by discharging it as deeply as possible in the beginning, before you recharge it.