If my battery is discharged -flat- the charger won't charge when I run it on my Honda 2000 watt generator. Partially discharged batteries charge just fine. Is there a voltage cutoff for my charger ?

Your description suggests one or both of the batteries are sulphated - been allowed to remain partially discharged or even fully discharged for a few weeks or more.

Charge the batteries, allow them to stand for a few hours and connect a voltmeter. A healthy young battery should read 13/13.2 volts while an older battery that is still serviceable might only achieve 12.7. Much below this and the capacity will be much reduced.

If these are the sort of voltages you have, the charger is probably ok. Ride the scooter until the battery indicator shows recharge is needed and test the voltage again - if it has fallen considerably, at least one of the batteries is faulty.

Traction, semi-traction or deep cycle batteries are the only ones that should be used and cheaper batteries will serve for a time but rarely survive the warranty period.
Batteries that are discharged generate heat when recharged and it is the heat that shortens battery life. Batteries last longer if they receive a top-up charge after each use.

Never leave a battery in a discharged or semi discharged state...

Try fully discharging the battery first and let it sit for a few days. Then fully recharge before use. What happens with battery operated drills is the batteries develop what is called memory of the charge level when they are recharged and will not charge past that point but the charge light will show full charge. It happens when the drill is used for a period of time and then the battery is placed in the charger ready for next time instead of using the drill until it is flat or leaving a partially used drill on the bench and not recharging it until it is flat

If the rechargeable battery is more than 3 - 4 years old then the battery could be worn out. Rechargeable batteries have a finite number of charge and discharge cycles and will lose their charge capacity over time, i.e. won't charge to 100% and gradually the charge reduces until the battery won't charge up at all. OR The battery shows a 100% charge but when the adapter is disconnected the battery drops off to zero capacity in a very short time. If the battery drops to an unacceptable charge level then the battery needs to be replaced. Rechargeable batteries will fail if stored in a discharged state for long periods.

if your battery is discharged it will get charged when the genny will start try to start through the recoil starter pulling the rope and check your engine oil level before starting

Most battery chargers are trickle type chargers - that is, they provide a constant low current (under an amp) output at 12 - 15 volts to keep the battery charge up. This small charging current is handled easily by a #14 or #12 wire which will pass up to 2 or 16 amps consistently, respectively (the larger cables off the battery are for the starter motor).

If you're having trouble maintaining a charge on the battery, a careful check of the charging circuit is required. Look for loose or corroded connections - at the battery in particular, open or blown fuses on the input (120 volt) side of the charger and the 12 volt output side (if provided). Battery acid is conductive. This means if there is a path of battery acid from one post to the other - no matter how long or short the path - the battery will discharge through this path. Neutralize (with baking soda) and clean any battery acid from the area to be sure the battery isn't discharging faster than the trickle charger can charge it. You can check the output of the charger with a DC voltmeter. Simply press the test leads to the battery posts and some value above 11.5 volts (11 - 12.75 volts may not be uncommon). Look at the chart below to get an idea of the charge of a lead acid battery



With the battery disconnect from the charger (or the charger powered off), the meter should show indicate 12 volts (even if practically dead) without a load. That's why it is important to load the battery when trying to get a voltage reading from it. Many auto parts stores sell and loan battery load / meters expressly for this purpose. They look like this:




If you have a battery that won't stand up under load, you may have a a problem with acid / distilled water level or even a dead cell. You can not check these variables in a maintenance free battery however. If you have removable caps on the battery, check and top off the level with distilled water only to a "full" or "high" level mark. A hydrometer can be used to determine the charge of each cell in the battery. These can be had for under $10 in most auto parts stores, too. They look like this:


Make sure you get one to check the specific gravity of battery acid - NOT to check anti-freeze level protection - they look similar.

Good luck!

I would say it can run fine without a battery. Make sure the battery cable terminals are taped up to prevent shorting out and damaging at minimum the charging circuit.

Go to the auto parts store and buy a "Battery Tender" solar powered, or get an electric trickle charger. Or install a battery disconnect for the period the unit is not in use; you can disconnect the battery.

HTH,
Mike...

Some Coleman generators have rectifier /diode pack behind panel others have a diode inside generator cover however when diode fails it usually fries the winding. Your winding could be within the generator or under flywheel depending on model#. If your generator had a fuse to protect winding then test diode and replace as necessary. You may also just plug a small battery charger (1 or 2 amp ) into 115v plug to charge battery / power coil. Good luck and email if you have other questions.

New battery for Honda eu3000is can be found on amazon. take a look here Charge your devices with guaranteed safety and chose the best one. P.S. watch out on seller reviews. I hope this was helpful. cheers