I have almost always selected Bosch batteries when there was a choice and they have given excellent service in a number of different cars. Batteries can be tested in a number of ways. i) Drop-test - needs the equipment to do it, but if you have it or can find a friendly garage that will test your battery you can tell there and then if it's any good or not. ii) Fully charge it (or leave it on charge for 36 hours or so) and then see what the voltage is an hour after ending the charging, 6 hours, 24 hours and 48 hours. It should stay above 12.65V - any less after 48 hours and it's discharging internally. Regarding current use while the car is not in use, you need to connect an Ammeter (as distinct from a Voltmeter) between one of the battery terminals and its disconnected cable (i.e. disconnect one of the battery leads and "bridge" the gap with the Ammeter). Most batteries in our cars are around the 70 Amp-hour capacity, which broadly means they'll deliver 70 Amps for one hour, or 1 Amp for 70 hours, or something in between. Given that I would expect a car to be able to be left for at least three weeks without being charged and still be capable of starting, this would argue that typical power conumption for a car that's switched off and just sat there should be around 0.1A or less. Certainly my 944S2 used less than 0.1A when this test was applied, at least after I found out why the discharge rate was unacceptably high. If you do find your consumption is over 0.1A, pull the fuses one at a time, replacing the preceding one before pulling the next one. When the consumption drops, you have located the circuit (or at least one of the circuits) where power is being consumed.
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