by Collyn Rivers
How to optimise RV batteries
This article shows you how to optimise RV batteries. It also shows how you can make RV batteries charge faster. It shows you how RV batteries store energy from your RV’s or tow vehicle’s alternator, solar, grid or generator power.
Flooded lead-acid batteries
Flooded lead-acid batteries need ongoing topping up with distilled water. If well-maintained, they have a long lifespan. They emit corrosive gasses. They are not suited as RV batteries.
Valve-regulated lead-acid batteries
Most RVs use valve-regulated lead-acid batteries. They are similar to flooded batteries. That sealing, however, is only nominal. There are vents that release hydrogen gas in the event pressure. RV batteries necessitate you housing them in a well-ventilated enclosure.
All lead-acid batteries dislike deep discharging. Doing so reduces their working lives. These batteries are relatively cheap. They are ideal for a quick ‘around Australia’. They are less suited to occasional RV use.
Now rarely used, gel batteries cost more than lead-acid batteries. Gel batteries can be discharged slightly more deeply. They cost more than valve regulated batteries. Gel batteries had a loyal following. AGM batteries, however, are more rugged.
AGM batteries were designed for military use. They are sealed, rugged and maintenance-free. AGM batteries, however, are bulky. A 12 volt 100 amp-hour AGM battery weighs about 33 kg (73 lb).
RV Battery basics dictate that routinely discharging AGM batteries below 50% shortens their life. They retain much of their charge, however, if unused for a year or so.
AGM batteries dislike temperatures above 40 degrees C. Do not locate close them to an engine. Furthermore, they are damaged by overcharging. Their self-discharge is tiny. Unless used routinely, charge them only every 6-12 months. Never leave an AGM battery on ‘trickle charge’.
AGMs cost you more than basic batteries. They are a good buy as RV batteries. Moreover, this is even more so if travelling extensively off-road. Furthermore, for RVs used infrequently.
For more about AGM batteries see AGM batteries for caravans.
These are a relatively new form of RV lead-acid battery. They are (so far) made by one company. Their main claimed benefit is 18 years, This may be so but is yet to be proven.
There are various types of lithium batteries. Those used in RVs are LiFePO4. This is their chemical make-up. They are often, but wrongly, marketed as lithium-ion in RV batteries.
LiFePO4s are a third the size and weight of conventional batteries. If fully charged, about 80% of their capacity is usable. This is about 40% more than most batteries. They supply and charge at massively high rates. Their output is 13-12.9 volts. This precludes lights flickering as fridges cycle on and off.
LiFePO4s are commonly used as RV batteries. Their main benefit as RV batteries is their low size and weight. An otherwise comparable AGM is a third of the price. LiFePO4 batteries, however, suit smaller and lighter RVs.
These batteries have individual cell monitoring and need specialised charging. They need specialised knowledge to buy, install and charge. Auto-electricians can assist.
It is not possible to forecast LiFePO4s’ future as RV batteries. Other batteries with similar specifications are under development.
For more about lithium batteries see Lithium batteries in caravans and motorhomes.
RV battery location
If used in a caravan (for stability) locate batteries close to (ideally just in front of) the axle/s. Never at its rear nor on its A-frame.
RV batteries are such that it is advisable to use a specialised alternator charger. To optimise charging locate that unit as close to the batteries as possible. Preferably not in the same compartment.
Battery makers advise that you vent the top and bottom of the battery compartment. There are, however, no industry standards. RV batteries dictate you have 25-50 mm holes at the compartment’s top and bottom. Or for you to use the stainless steel vents sold by boat chandlers.
An external battery compartment door should be of a light colour. It also needs heat insulation.
RVs need batteries close to the alternator but protected from exhaust heat. Connect them to the alternator via at least 10 square mm cable. It is advisable to use a dc-dc alternator charger. LiFePO4 batteries need a specialised low-voltage version.
RV battery capacity
Battery capacity is expressed in amp-hours. For 12 volt batteries, to convert amp-hours to watt-hours multiply by 12. For 24 volt systems multiply by 24.
RV batteries can be seen as (fee-charged) bank accounts. They hold energy paid in and release energy drawn out. In doing so, they lose energy internally. That lost is 15%-20% for lead-acid battery, but only 1%-2% for LiFePO4s.
As with bank accounts, RV batteries preclude you from storing or using more than you pay in. You incur overhead fees if you add another account (i.e. another battery).
Unless increasing energy to store, do not increase battery capacity. Doing so is like adding a further bank account for the same income. That second battery increases storage losses. Many RV owners misunderstand this. RVs owners who run out of 12-volt power typically buy a new battery. Some add another. Doing this only works if there is excess energy for charging.
Limit battery capacity such that they fully charge on most days by noon. This typically requires about 250 watts of solar per 100 amp-hour battery capacity.
There is next to no risk of you overcharging. Alternator regulators and solar regulators control charging voltage. Moreover, LiFePO4 batteries accept far higher charge currents than your RV can supply.
Use batteries that suit your pocket, weight carrying ability and needs. Maximise solar capacity. Doing so enables you to charge them even via light cloud.
You should never mix battery types. Furthermore, do not add batteries unless they are of identical capacity, age and type.
A few RV owners use a generator to run a CPAP (sleep apnoea) machine. Instead, use a generator or solar to charge a truly reliable battery during the day. Furthermore, run the CPAP from that at night.
Further information about how you can optimise RV batteries
Optimising RV batteries is covered in-depth in our book Caravan & Motorhome Electrics.