Updated 2020

Battery Charging via Generator

Battery charging via generator is often slow and shallow or barely works at all. In many a campground, mobile generators run all day in vain attempts to fully charge their RV battery from the 12-volt output of their 230-volt generator. Even if marked ‘battery charger’, that output is suitable only for running small 12-volt lights and appliances (directly) without a battery. This article shows how to speed it up..

Here’s how to fully and speedily charge a battery from a 230-volt generator

Fully and speedily charging a battery via a 230-volt generator is feasible. You do it by using a high-quality 230-volt battery charger run from the generator’s 230-volt output.

A typical mobile generator’s nominal 12-volt output while charging a typical RV’s battery is about 13.6 volts. That voltage may bring a flat 100 amp-hour battery to half charge within 5 or 6 hours. But that’s about all. After that charging virtually ceases. That 13.6 voltage is far too low for fully charging that battery. It may reach about 70% charge after running for about 24 hours, but even longer for deep-cycle lead-acid or AGM batteries.

Honda 2000 watt petrol generator produces up to a constant 1.6 kW. Pic: Honda

Battery charging via a generator – the type of charger that’s needed

Most portable generators maintain their rated output for only a few minutes. Their continuous output limit is usually 80% of that claimed. In reality, your 1000 watt generator is an 800-watt generator. That is nevertheless sufficient to power a quality 30-40 amp charger. A generator of that size fully-charges a fully discharged 12 volt 100 amp hour lead-acid, AGM or LiFePO4 battery within 3-4 hours.

Avoid buying a cheap generator. Do not even think about doing this with a $99 chain-store special. Such generators are noisy and polluting. Worse – their electrical output is ‘dirty’. They can and sometimes do damage so-called switch-mode battery chargers (or may not even run them at all).

High-quality RV battery chargers are not cheap. Expect to pay $350 upwards. Do not skimp on this. Any savings on a cheap battery charger is wiped out by its inevitable inefficiency. That requires running the generator for longer, thus using more fuel.

Furthermore – some cheap battery chargers can destroy batteries. Few can withstand over-voltage charging. High-quality chargers work quickly and reliably. Some top brands are better than 90% efficient.

Battery charger Xantrex 201 smallHigh quality Xantrex charger is not cheap, but charges fast and safely. Pic: Xantrex

Problems with switch-mode battery charging via generator

Issues may arise with a generator and switch-mode inverter-chargers (these are smaller and lighter than transformer-based chargers). Switch-mode chargers are reasonably efficient. Some, however, work fine from grid power, but not some generators. Switch-mode devices work well but need ‘clean’ electricity.

A cheap generator’s output is usually ‘dirty, and particularly so if it runs out of fuel and sputters to a halt. If this happens, it usually causes the switch-mode charger’s protection circuits to cut off the supply, but may even wreck the charger.

Resolving this problem varies from difficult to impossible. Generator vendors usually deny responsibility because their products drive most electrical loads without problems. Battery sellers too may deny responsibility. Their products work fine on clean electricity. Each thus blames the other. This issue is mostly past – as many RV owners buy the quiet inverter type units. These usually work well with switch-mode chargers.

Our associated website – solarbooks.com has many articles on a caravan, motorhome and solar home and property systems.