Disco 3 (LR3) Battery charging, stupid question.

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I shafted the battery on my td5 defender welding with it still connected.

Always welding trailers at work, all have fridge engines, and battery never gets given a thought, in fact I only thought about it as I read your post!
Most are small fast welds, not often longer than 6 inches.
 
The thing is that it's enough to be unlucky once in a lifetime with an expensive vehicle then you'll remember the bill

They are all expensive and all very very complicated, we cannot even test some of the wiring as they run on pwm signals and we do not have the kit.
 
The requirement to keep the weak battery connected when jump starting is for a completely different reason and cannot be compared to charging a battery with an external charger. We do jump starts to start the motor and as soon as this happens, the alternator starts producing energy. Alternators do not like an open load and without a proper current sink to absorb that energy, it can easily burn out. Modern vehicle electronics will suffer the same fate from spikes and transients currents that are normally absorbed by the battery, acting as a huge capacitor.

Charging a battery with an external charger is the complete opposite as the motor is not expected to run until the battery is fully charged and reconnected.
...which is also why when jump starting a vehicle from one that is running, the running vehicle should switch on all the stuff, i.e. heater fans, lights rear window heater etc, so the sudden loss of load when the other vehicle's batt is disconnected doesn't upset the running vehicle's alternator.
It used to be possible, in the days of dynamos, to take a good batt off a vehicle, remove the flat batt off another vehicle, connect the good batt to the one with the flat batt, start it then leave it running while you swapped the batts over again. But do that with an alternator and you are asking for trouble.
God I am old! :):):):):)
 
The requirement to keep the weak battery connected when jump starting is for a completely different reason and cannot be compared to charging a battery with an external charger.
It's much the same, although the risk of damage with jump leads is higher. Power from a fully charged battery is supplied via the jump leads to the dead battery, in the same way that power is fed from a battery charger to the dead battery. If hundreds of Amps supplied by jump leads doesn't do any damage, then a few Amps supplied by a toy battery charger won't. ;)
Modern vehicle electronics will suffer the same fate from spikes and transients currents that are normally absorbed by the battery, acting as a huge capacitor.
Precisely, which is what I said initially. The battery will absorb any tiny transients from this tiny battery charger, so it's perfectly safe to keep the battery connected.
 
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