rechargeable lead acid batteries

hi,

I'm designing a DIY emergency light for some places in my house as I have quite a lot of power problems here, anyway, I was thinking, can some one help me out with the following questions regarding batteries:

1. I was thinking of getting the 12v 4aH battery, **broken link removed** at rapid. Does it mean I can run a 12 halogen 20w light bulb for 4 hours or whatever? what is the maths? it says it can supply 200ma for 20 hours, does that mean I can get 1amp for 2 hours or something?

2. what kind of rated relays do I need to make sure it can handle the current from these batteries?

3. what kind of charging circuit do I need to charge these from a +12v 400ma powerpack? would that mean it takes 10 hours to fully charge?

4. I assume that a 10w halogen light would use half that power/have double the time...

5. what are suitable 'tab' connectors? any part numbers?

thanks for your time,
computer

ps: incase you are wondering I am using a simple relay controlled by a microcontroller to run it....

1. If the battery is rated 4AH at 200mA, it will provide less than 4AH at 2 amps. 1 amp for 2 hours should be no problem.
2. You should provide a saftey factor of 2X the load.
3. The nominal battery voltage is 12.6 volts and it is fully charged at 13.8 volts. If you power pack is only 12 volts, it will not fully charge the battery.
4. Yes, less current, more time, but since the battery is more efficient at lower current, the time may be slightly more than double.
5. Not sure what you mean by "tab" but check out Mouser part number 517-2250 and 517-2187

well rapid says in the description it is provided with tab connections... I'm looking for a suitable rapid mating plug/socket....

I also have a 15v 1amp charger, how can I hook that up to make sure I don't over charge?

The connectors on this type of battery is typically called a 3/16" push on or quick connect ..you can find them at any electronics shop..

Two 1 amp diodes in series will drop the voltage to 13.8. 1N4001 will work