Laptop batteries commonly have four 36v li ion cells in series to achieve a nominal voltage 144v and two in parallel to boost the capacity from 2400mah to 4800mah. When connecting or charging batteries in series your goal is to increase the output of your batteries nominal voltage rating.

Can I Charge In Parallel Run In Series At The Same Time
Charging batteries in parallel. What does this mean to you. Two 12 voltbatteries in parallel one 12 volt charger figure 9two batteries in parallel one charger batteries connected in series strings can also be recharged by a single charger having the same nominal charging voltage output as the nominal battery pack voltage. Batteries may be wired in parallel or in series. This method of charging batteries in parallel will result in each battery drawing the same amount of current from the charger. Two 12 volt batteries wired in parallel continue to produce 12 volts but the capacity doubles. Two 12 volt batteries wired in series produce 24 volts but the capacity remains the same as one for a 12 volt battery.
Connect the positive output of the charger to the positive terminal of the first battery and connect that positive terminal to the positive terminal of the second battery. Parallel connection attains higher capacity by adding up the total ampere hour ah. In a nutshell parallel charging allows for multiple same cell count batteries to be connected in parallel to create a single larger logical battery that can then be charged. All you need do is to follow the safety precautions associated with the charging of lithium ion or lithium polymer batteries. The batteries are connected in parallel hence the name parallel charging. When charging batteries one by one you have to repeatedly unplug a battery and plug another one in between charge.
This method of charging can be utilized when there is an even number of batteries 4 6 8 etc. Charging 12 volt batteries wired in parallel requires a 12 volt battery charger. If you do not know how this works you either find someone who can do it or you dont try it at all. Yes batteries in parallel can be safely charged. Say you have 3 3s 2200 packs that you run in your 450 sized heli. For secondary rechargeable batteries the stronger battery would charge the weaker one draining itself and wasting energy.
Some packs may consist of a combination of series and parallel connections. Parallel charging is a fast and easy method to charge multiple lipo batteries at once with just one single charger. In figure 8 a single 24 volt charger is connected to a 24 volt battery pack. It will maximize the lifespan of all your batteries as they will be charged and discharged evenly. To do this you need to connect the pos terminal of the first battery to the neg terminal of the second battery. If you connect rechargeable batteries in parallel and one is discharged while the others are charged the charged batteries will attempt to charge the discharged battery.
An example method of charging batteries in parallel is to use one branch of the parallel circuit to charge each battery with a single charger.