Trickle charger starting an empty battery

1995 V-12 VJS Convertible.

My trickle charger got unplugged and the battery drained.
When I restarted the trickle charger - about 60s later a clicking sound (not grinding, a steady click-click-clicking) started under the hood above the left front wheel. The charger indicated de-salination, and I thought it may have something to do with the radiator overflow system which is near the clicking sound. About 5m later - the clicking sound stopped. What is the cause and explanation as I’ve had the battery drained before without this incident. Thank you for looking.

Unless you have an extremely rare ocean-going XJS, I am going to hope that your charger is actually de-sulfating and not removing salt from sea-water. The clicking- no idea.
Radiator overflow should have nothing to do with your electrical system.

some trickle chargers can deal with a totally depleted battery, some can not, some have many smart features…7 steps, some have none. The CTEK 5.0 can do a lot…but still a full charger for dead batteries is different than a trickle or maintainer. I don’t know of one that makes noises…usually lights or led, but maybe there is one–go to the manufacturer web site, check your model. But–again, most maintainers are not good at total discharge.
Nick

All I can think of is one of the relays possibly?

Hi, it was the relay - not sure which one yet. Good news is that the battery re-charged just fine.

are you sure it was a relay in the car, and not the trickle charger itself ?
some of them uses a specific charging pattern to help and reduce the lead sulfates from the battery plates
my Noco has such a feature :

The charger is in the boot with the battery - the clicking is from above the left front wheel where there are relays.

so clearly no possible mistake

iirc, the relays at the front left are

  • headlamp logic module (bigger box, black)
  • empty red socket (iirc used for german market)
  • headlight relay
  • fog lamp relay
  • side light relay
  • electrical fan relay

that’s for th 94 MY, so could vary for a MY95

From front to rear, the 95 Tech Update shows them as

Aux Fan
Side Light
Front fog light
Headlight
Air Injection Pump
Headlight Control Module

Anyone of which, if its. control was left ‘on’, would ‘click in to NO’ when voltage was sufficient, ‘click out to NC’ when voltage dropped below its limits.

Which could result in a relay trying to ‘click in’ (pull coil in), then drop back out

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Or, if it ever happens again, disconnect the battery cables and attach the charger cable s directly to the battery posts.

CHJ

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Or put a decent 35 amp charger on it for a few minutes first, then go back with the trickle charger.

I’ve found that sometimes a battery just needs a jolt to ‘wake it up’ so to speak.

Has worked several times for me.

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