Battery issues with SB and LB

[Rebiam]

Hi all - expert assistance required? I have a winter set up where I am currently using the existing second starter battery as a LB (with willington kit fitted). A couple of times the SB has gone flat when stopped and using what I thought was LB to charge my phone and listen to the radio for a short while. I was assuming the relay switched over to the LB. On all occasions I have just disconnected the LB lead and put back the original series lead and started the engine. Today when it happened I put a meter across both batteries and they were both reading just over 12.8v when the engine wouldn't start - (not enough juice in the battery to turn the engine). After swapping the leads and starting the engine they are both showing 14v with the engine running. I also have a bit of corrosion showing around both battery straps but the terminals and earth are clean and corrosion free.
How can I tell if my relay is working?
Do I need a new SB and LB as my existing set up has run its course?

Cheers

[cmm303]

The Willington kit allows the LB to charge when the engine is running but isolates the LB when not running. However this does not switch circuits coming off the SB to the LB so if your radio and 12v sockets are connected to your SB then they will always run off that battery whether the engine is running or not.

You could run the radio and 12v socket circuit off your LB to avoid them draining the SB.

[Rebiam]

Cheers Chris - radio, 12v sockets, interior lights and blinds running off LB (I think). They all work with no key in the ignition.

[cmm303]

That does sound like the usual 4 circuits have been transferred to the LB. With the Split Charging relay lead (not the old second SB lead) connected to your LB, your SB shouldn't go flat. If this is only a problem when camping then I would check that these circuits really are coming off the LB and if the Split Charging Relay is isolating the LB. Does the relay have a (green?) LED that comes on when the engine has been running and goes out a while after turning the engine off.

If your SB drains when just parked at home then need to investigate a drain on the battery or its condition.

[Gasy]

Have you disconnected the old second battery positive terminal from the second battery

Are the 2 batterys separate now

[g8dhe]

If the relay was staying operated, then both batteries would be in parallel already, so linking them back together again would make no difference. This suggests that the SB is going flat on its own, and that the relay is doing its job correctly, isolating the L/B from the S/B so its retaining its charge quite happily.
I would suggest you use a current meter to check what is being drawn from the S/B when the ignition is OFF and then tracing down the rogue circuit drawing the current.

[scanner]

If BOTH batteries were reading at 12.8V, I am very puzzled as to why the engine wouldn't start.

[Rebiam]

Thanks all - spent most of yesterday trying to work it out as the engine starts fine now. I did find (concealed under the steering column cover) a "turbo timer" which was switched off but still had LED display. This has now been disconnected and binned. The batteries both retained 12.8V overnight. No other unexpected drain on the batteries, and the split charge relay has a green light on so I am assuming no problem with that. Could the problem be something other than the batteries like the starter motor solenoid? Not had a specific problem but have noticed very occasionally a delay between turning key and the starter turning, and sometimes there is a similar delay when turning the key and the electrics inside the cabin turning on - heater fan noise. The radio is always completely turned off (make sure of that as it runs on the LB and I have one with a standby option showing clock or completely off).

So when the failure occurs the engine turns over very slowly, not enough to fire and all the electrics fade. The radio still works and so I can see this is being run from the 2nd SB which I use as a LB. When I connect the 2 in series then there is no problem starting. I have noticed that when I reconnect the relay lead the voltage in the SB comes back quickly. Am I safe to assume that I need a new SB? They are both Japanese batteries, are the same and look old, and I have been topping them up monthly.

Is the corrosion on the brackets that hod the battery anything to be concerned about? Cracked somewhere?

[g8dhe]

That does start to sound like a well used SB with the full description, why not swap the old second SB to the first position and replace the LB with a proper LB. The older SB might not last long but then you will end up with two new batteries and know the state of them both from then on.

Perhaps check the -ve terminal and the chassis connection on the current SB it might be corroded, before the above.