Increasing Your RV Battery’s Capacity and Overall Runtime
On Overlanding adventures where primitive campsites don’t have power hookups, your house battery may not be large enough to provide the power you need for the length of your stay. On these occasions, one definitely does not want to run out of power for lights, cooking, or charging mobile devices. So if you’re venturing out into areas without power to plug into, it’s easy to add more battery power and run time if you have space.
Deep-Cycle Batteries and Amp-Hour Ratings
Many RVs come with a single 12-volt battery dedicated to the unit’s house power. To increase the capacity, you first need to make sure the battery is a deep-cycle model. Some RVs are outfitted with a typical automotive starter battery which works fine to provide lots of initial power to start an engine, but not for maintaining power over several hours for lights and other electrical accessories. Switching to one 12-volt deep-cycle battery is a start. It will provide power for a longer period of time, indicated in amp-hours (usually the 20 hour capacity in Ah).
Amp-hour ratings are shown on the battery label and will help you figure out how many discharge amps the battery can provide for however many hours you need to supply. Here’s an example. The most common rating is the 20 hour capacity in Ah or rate in amps. The capacity in amp-hours is found by multiplying the discharge time (20 hours) by the discharge rate. The discharge rate is found by dividing the rated amp-hour capacity by the discharge time (20 hours). For example, a battery that is rated at 100 amp-hours at the 20-hour rate would have a continuous discharge rate of 5 amps for 20 hours. Similarly, a battery with a rating of 100 amp-hours at the 5-hour rate would have a continuous discharge rate of 20 amps for 5 hours, but its 20-hour capacity would be much higher than 100 amp-hours (probably closer to 130 Ah at C20). When selecting a battery for a given application, it is important to use the rating that is closest to the average runtime needed between recharges in the application. That, combined with knowing the total amperage your electrical accessories in your RV will draw, will help to determine how much battery capacity you will need.
Two-Batteries Are Better Than One
If you switched your house power to a deep-cycle battery with a greater amp-hour rating but find you still need more capacity, you can add another battery in parallel if you have space. Adding a second deep-cycle 12-volt 100 amp-hour battery connected in parallel, for example, will keep the voltage the same at 12 volts but will increase the capacity to 200 amp-hours. This can double the discharge rate (10 amps for 20 hours) or simply run the system for a longer time between recharges.
If you have a large enough space in your RV to add more batteries, you can add a third 12 volt – 100 Ah battery connected in parallel. However, it is not recommended to make more than three parallel connections. If even more capacity is needed without increasing system voltage, another method is to connect 6-volt batteries in a series/parallel circuit. Six-volt golf car deep-cycle batteries are designed with much higher capacity per battery. (200 – 250 Ah each).
Two six-volt batteries can be connected in series for 12 volts and then another set of two connected in parallel for 400-500 Ah or a third set in parallel for 600-750 Ah at 12 volts.
The difference in wiring batteries in series and parallel can be seen here. If you plan on attempting this upgrade, make sure to use high-quality large-gauge wiring and connectors, and talk to an RV electrician for any help in setting up a multi-battery bank system. Some systems like this need to be separate from the RV’s charging and electrical system. It will also require you to use a good-quality battery charger specifically for large capacity deep-cycle batteries. If Overlanding is a long-term lifestyle, many have also considered adding solar panels to the top of their RV to keep deep-cycle house batteries charged and provide consistent power when they need it.
While upgrading to more batteries is more expensive, the larger battery bank will lower your depth of discharge (DOD) on each battery to the recommended 50% or less. This will ultimately enable the pack to last much longer than constantly draining a single battery.
