Charging Battery Directly

[ehoe]

I have a portable Bosch 12V car battery charger which I want to use to charge my battery that is a little weak. Question is can I attach the charger directly to the battery and charge it or would it be recommended to disconnect the + and - terminals first then charge the batt?. Don't wanna fry any electronics by attaching directly to the batt and charging mah. I have heard some say its ok to charge directly whilst some saw better to disconnect the batt first. Any experts out there know the correct way?.

 

[jarance]

Actually, it depends on the voltage output of the charger. Even though it states 12V Dc, chances is that the voltage output could be at least 1.2 X 12 VDC. Some of the charger comes with "boost" charge and "trickel" charge mode.

In the boost charge mode, the voltage is higher in order to quickly charge the battery. Normally you use this mode when the battery is nearly flat and need a quick charge. However, this mode is not recommend as it will not fully charged the battery. The normal output voltage can sometime be as high as 1.4 X 12 V DC = 16.8 VDC.. Because of the high voltage, it might not be recommend for some electronic ae they are rated to +/- 20 % tolerance.

Note: If you plan to stored your battery after charging, do not use boost charge as the charge does not retained too well when the battery is charged in this mode.

In the trickle charge, the output voltage of the charger is lower. Normally about 1.2 X 12 VDC = 14.4 V DC. This mode is recommend in most case as the battery tends to retain it charge better. However, the duration is longer due to the slow charge.


Note: There are some chargers that have auto charge mode. i.e. it can start charging the battery on boost charge first and switch to trickle charge when the voltage and current draw is less from the battery.

Most of the battery used by cars are Lead Acid type. There are some manufacturer who produce maintenace free battery but they are relative slightly more expensive than the conventional type.

My advise is to disconnect one of the terminal from the car battery when you intend the battery with a portable charger. Make that the area is well ventilated as the battery gives off acid fume during charging.

 

[jetschin]

By the way, what is the best way to maintain the battery charge if the car is going to be left undriven for say, 2 or 3 weeks? Some say it is best to disconnect the negative terminals to maintain the charge. What about having someone to drive it around every 2/3 days?

 

[KiNaKa]

disonnect the negative pole :-

- no need to send the car to anybody.
- need to disconnect the battery pole by urself.
- but need to reset ur clock & radio station when u are back.
- car didn't start, rust will start to work. basically not much becoz nothing is
dismantle just that cooling circuit such water tank, but no worries if
circuit contain coolant.

send it to people :-

- waste some time to send and collect ur car.
- car being started everyday, function as usual.
- don't know whats going to happen on ur car.


hope this help...

 

[bmwky]

Originally posted by jetschin@Nov 9 2005, 11:22 PM
By the way, what is the best way to maintain the battery charge if the car is going to be left undriven for say, 2 or 3 weeks? Some say it is best to disconnect the negative terminals to maintain the charge. What about having someone to drive it around every 2/3 days?

A trickle charge is what you need to keep your battery healthy if the car is not used for some time. no need to disconnect the terminals.

 

[E34EuroTouring]

No need to remove the terminals. Just put +ve to +ve and -ve to -ve on charger and plug in overnight. I have been doing this for years in my second E34 that is driven once in 2 weeks or less.

This is a trickle charger so if the battery is 10.75 volts, it will climb to 13.86 volts and stay there for whole night. Next day. A good voltage of 13.80 is stable on the battery. This can last for one month or more with alarm on and some minor drain on some internal electronics. My E34 has 2 alarms, an AutoPage alarm and a GSM Phone alarm so it holds standby on a phone for a whole month and still can start at 11 volts!.