Not Always Available
Generators provide AC power and are capable of high outputs for extended periods of time. Batteries put out DC power and can only provide power for short periods of time, making them a poor choice for generator backup. Trying to back up a generator with a battery is generally an expensive and impractical proposition, especially for the home. Does this Spark an idea?
A home in an isolated area using a generator for primary power could use commercially available battery backups for a few individual appliances, but not for the entire house. In a home with commercial power, where the generator only backs up the house during power outages, the batteries would be used only if the generator failed during a power outage, and could only protect a few small appliances for a short time. If the generator is intended for an RV, there may already be a battery that the generator keeps charged.
Backup of the entire house would require an impractically large battery backup. Refrigerators, freezers, stoves, dryers and heaters may be out of the range of power available with anything less than a huge, industrial backup battery. A battery plant this size would need constant charging, venting and periodic maintenance. For backing up smaller items like computers and emergency lighting, commercially available individual backup battery sources are a better option than trying to back up the generator.
Inverter and Transfer Switch
If a homeowner decides to buy a huge industrial battery plant to back up his entire house in case of primary or standby generator failure, he should also purchase an industrial-size inverter to change the DC from the battery to AC. In a commercial power situation, where a standby generator is wired to a transfer switch, a third input would be needed to accommodate a third AC input.
The Rectifier or Charger
A rectifier or charger changes AC to DC to keep the backup battery on constant charge. It must be of industrial quality and therefore will cost a relatively small fortune. A generator used on an RV may already have a battery and a charger. Many RV appliances run on either AC or DC and already have a charger for both the battery and operating the electrical equipment, regardless of whether its input comes from a power line or a generator. In the event of a power failure, the battery simply takes over the load as if there were no input.
In a home, a second generator is a more practical backup for an extended power outage. Computers and small appliances can be protected with low-priced battery backups that come with inverters and chargers already installed. For emergency lighting, kits with all equipment installed–battery, charger and light bulbs–work well. For an RV, a second or a higher-power battery to replace the existing one would be far more practical that trying to back up the generator with an entirely new backup system.