Tool suggestion please

How odd starting a post in technical! 

Need a recommendation for a recording or data logging oscilloscope. Needs to be affordable and simple enough for a mechanic but it's got to be able to record for like a weekend so that I can see what if anything is either not sleeping properly or waking up when it shouldn't. Not strictly for jimny related shenanigans but 4x4 related. I know there's a lot of definitions on affordable but it needs not be so cheap that it let's the smoke out first time I connect it, but equally I'd rather not buy a fluke level one either as it's mostly going to sit on a shelf as I'm not yet running a paying garage.  What is there? 

Update. Don't really need a full scope so much as a data logging ammeter if you know of any, preferable with at least a week or so of recording?

There are plenty of cheap multimeters about that will output data on a USB lead, but I suspect that they will go to sleep after a few minutes and the battery won't last long.

I did spot the OWON B35T+  and OWON OW18E (I think you want a OWON OW18B for Bluetooth logging)  that claim to support 10,000 readings via bluetooth from your 'phone (so one every 10 seconds would cover 24 hours) but I couldn't figure out if it wakes the meter up to read, it ought to or it wouldn't be much use. There was mention of it overwriting the reading too, so I suspect your 'phone has to pull the data every 10 seconds., 

I take it you want to monitor battery current over 24 hours to see if the ECU refuses to go to sleep or comes on for an hour at 2AM (We had a Merc 190 that did this, and tripped the aftermarket alarm at 2AM).

What you want is a meter that can store 10,000 readings, that you can set to come on and measure every 10 seconds, then just download the stored data via USB and analyse it, but I don't know of anything cheap that will do it.  (You'd think that you can't be the only person in the whole wide world who wants to do this!) All the cheap(ish) loggers log temperature & humidity and won't do what you need.

A proper general purpose logger that can measure voltage (and therefore current with a suitable shunt or a Hall probe) would cost a couple of thousand.

This is just the sort of job for an Arduino, they have analogue inputs that count to 1023 at 5V in, with a bit of input circuitry you could make a 10A meter with 10mA resolution, then write something that wakes it every 10 seconds and stores the reading. To flatten the battery in a short time it is going to be a couple amps for minutes if not hours at a time, so should be easy to catch. The only problem is arduinos don't have enough storage, and adding SD cards is a pain. A Raspberry Pi has the storage, but you have to build a separate analogue to digital converter.

Try downloading the manual for one of those OWON meters and see if you can make it do what you want, otherwise it would be a nice project for tinkering with an Arduino kit.

Alternatively, get a battery isolation switch and cut the battery off when you park!

It is interesting like you say that I appear to be the only person on the planet that doesn't have a thousand pounds to spend trying to chase this type of problem. The car is on an isolator and also a mains conditioner so the problem whatever it actually is isn't mission critical but it would be nice to be in a position to elect to put it on charge because I'm not planning on using it for a month rather than having to manage it so that I can use it. Programming is way out of my ability range, know these little boxes exist but I have no idea how to make use of them. I'll download the manual and have a read.

For the record the problem is 7 starting batteries on an 8 year old car. It's been on going since we bought it 5 years ago. It's been through the dealer and distributor workshop for several months at a time including being compared against another virtually identical car. It's been to 3 independent auto electrics specialist workshops for weeks at a time and no-one has been able to find anything wrong with it. But still it's given a new battery and after about 3 months said new battery is struggling to hold charge and then after a couple more it's needing a booster even if it has done a hundred miles the day before. Somehow it is producing a situation where I think it is actively sulfating the battery. Hence it is isolated and the battery is on a mains conditioner. It's a land cruiser and those are supposed to be the epitome of dependable.

I have CTEK Battery Sense fitted to both my cars. It’s a little datalogger which measures battery voltage and temperature, with a phone app that connects via Bluetooth.

I think the CTEK holds about 3 months worth of data, recording every 5 minutes 24x7, it’s a fit and forget.

CTEK discontinued it a couple of years ago, but you can still find them for sale new as old stock.

There are other ones which do the same, E.g. Victron.

I know it’s voltage and not current, but you can tell if current is flowing as battery voltage suddenly goes down.

I also have an Owon multimeter with BT output, I have used it to monitor current on a vehicle in standby (using the phone app) but couldn’t say how long it will run for and then you need a phone connected and logging all of the time.