This is directly on the battery. I already have a cTek connector under the bonnet. I am going to a monitor and charging cable on the battery. SDV8 AB MY 2020
MINI Cooper S Cabrio
Kit: Jaguar XK140 (in progress - the website is link to build)

………. “If it ain’t broke, don’t fix it” -where’s the fun in that?

Last edited by Gremlin500 on 18th Apr 2024 10:23pm. Edited 1 time in total

So on the main battery, I have connected a monitor. I will order another one for the second Battery. Just to really see what is going on.

Is there any documentation about when both batteries are connected together? E.g. if voltage falls under a value? when the car is on terminals under the bonnet? I have a strange graph for the overnight voltage. it drops and then jumps up and slowly drops again.

I thinking about some of the readings that I got when charging the car using the terminals under the bonnet. The higher charging voltage was only on the secondary battery, not the main one. So I now think that I will also charge the main battery directly at times.

The voltage reading under the bonnet is higher than the main battery but lower than the secondary. When I was doing these reading the car was active so the batteries were in parallel. At other times they are separate and supply different circuits.

I like trying to get to the bottom of a puzzle. SDV8 AB MY 2020
MINI Cooper S Cabrio
Kit: Jaguar XK140 (in progress - the website is link to build)

The main battery was replaced today. With the GAP Tool (Beta), the action of the main battery replacement was done.
The battery monitor is reading 12.52V. I need to drive the car a bit more or I might charge the battery overnight.

To have peace of mind I have ordered a new secondary battery, I can hopefully replace that on Friday. SDV8 AB MY 2020
MINI Cooper S Cabrio
Kit: Jaguar XK140 (in progress - the website is link to build)

So I have disconnected the charger. I am watching the voltage of the main battery via the App. It has a reading of around 12.8v. Which is so much better than the old battery. I will fit the other battery and monitor on Friday. I am happy that I have done this. SDV8 AB MY 2020
MINI Cooper S Cabrio
Kit: Jaguar XK140 (in progress - the website is link to build)

………. “If it ain’t broke, don’t fix it” -where’s the fun in that?

Last edited by Gremlin500 on 18th Apr 2024 10:23pm. Edited 1 time in total

So I fitted the second battery today. The Breather pipe doesn't fit into the battery, they changed the clamp in the later car and the battery from Land Rover has the breather hole offset. So either I drill a hole in the clamp or go for an original battery.


On the main battery, it was going well. But part way through the journey today (looking at the monitor) the battery was no longer charging. So at the end of the journey. 3 trips of 40 minutes each. The battery was in a lower-charged state. I think it will be hard to find this issue. I need to do a long journey tomorrow for the Active ReGen I will keep an eye on the battery levels. SDV8 AB MY 2020
MINI Cooper S Cabrio
Kit: Jaguar XK140 (in progress - the website is link to build)

Be careful not to 'over think it ', the alternator is a smart charger so I am guessing at times it lets the battery drop to a predetermined level?

The main battery was at 12.9V when I started the 3 trips and 12.2V when I finished. That is the part I found odd. SDV8 AB MY 2020
MINI Cooper S Cabrio
Kit: Jaguar XK140 (in progress - the website is link to build)

I would have thought that was ok, the monitoring system managing the charge between set upper and lower limits? Maybe someone with more knowledge could confirm as it would be usefull to know.

Charge level (not voltage) is intentionally maintained ~80% which would fit with your recorded voltage - some of which will recover once the vehicle is 'sleeping' The key thing is that the generator can support the vehicle load andcharge the battery as required. A new battery will most likely be above 80% charge - and if the BMS has been reset, then there will be a learning period.

I probably should know this my car doesn't have stop/start but I am thinking a new battery is a good idea (wouldn't start today in freezing conditions) its an early L405 so I am assuming its AGM but does anyone have any specific recommendation? Geoff

Bosch S5A13 019 is standard size fit, you can squeeze an S5A15 020 in for max. amps - just.
Although mine is non-autostop, I've not had any issues with voltage dip on cranking or FBH preheat not running or shutting down prematurely. It costs more than a standard AGM but IMO worth the extra for the lack of low voltage issues and anomalies that 'just happen' I don't do a lot of miles for five days a week so I wanted something that was resilient enough to stand up to winter temperatures and usage before it got a decent amount of use at the weekends.

Quick follow up question, the handbook says remove the battery to charge it. That will be a royal ballache or at the very least backache so can I just connect my c-tek to the jump start terminals under the bonnet. Geoff

Yes you can. I have a Ctek quick connect attached to them. It charges the battery well. SDV8 AB MY 2020
MINI Cooper S Cabrio
Kit: Jaguar XK140 (in progress - the website is link to build)