There are several ways to to handle field charging, and if charging multiple batteries at one time a portable generator is the best. You’ll have to adjust your travel schedule to suit the task.
Something that may not be obvious even when charging just a single battery, a 1c charge rate will take close to an hour to replenish a discharged battery. Even when only partially depleted the charger will reduce the charge rate to suit the charge state of the battery so even at 1c you’re looking at close to an hour to replenish a half charged battery.
Another factor is available amperage to supply a multi port charger. As an example, if you have a 4 port, 20A charger, that amp rating does not mean the charger will deliver 20A to each port when more than one battery is being charged. (20A was used as that is what most house circuits are provided). The available amperage will be divided up by the number of ports in use so if you are charging 4 batteries each port will be capable of delivering up to 5A for charging. Now the tricky part. If the power supply for the charger is not capable of providing a full 20A to the charger the current available to each port in use will be reduced to that which is available. Say you only had a current supply of 10A to the charger there would only be 2.5A provided to each of the 4 ports in use. Your 1C charge rate will be reduced to less than half if what is needed to charge a (example) 6000mA battery at 1C so they will take longer to charge. Bear in mind your car’s cigarette lighter or USB port is likely only a 5A circuit
. Check the size of the fuse used in the circuit or the vehicle owner’s manual to determine what the maximum amperage is. If you elect to use a generator, which is the least abusive method for your car’s electrical system, you’ll need to size it based upon the needed demand.
Next route would be to install a power inverter in your vehicle’s charging circuit for use when the car is running. One large enough to handle a 4 port charger will be kind of pricy. You don’t want to charge a bunch of batteries with the engine off as the car’s battery can be depleted to a state where it will no longer start the car. That can happen fairly quick when trying to charge a lot if batteries.
Another option is to carry a long (14awg minimum) extension cord to use with your charger when a wall outlet might be available. It never hurts to ask a customer if you can charge some batteries at the site if such could be done.
Any way you go there has to be enough available current to meet the demand. If the current isn’t there the charging cycle will take longer. The more batteries we need to maintain the more we have to look at stepping up with the peripheral we need to maintain them in the manner we need them handled. It can get complicated and expensive. Big aerial outfits haul trailers equipped with all they need for maintenance to sites. That doesn’t work for the small operators but it shows we have to plan and allow for what we need to keep on hand.)
I have a small 1200W two stroke generator to handle minor battery charging and a 3500W generator for use on trips where I’ll be “away” for several days. The small one is good for a two port charger but does require over an hour to get it done. Remember to adjust the time cut off in your charger to longer than 90 minutes to prevent early termination of a charge cycle.
