We are having some starting issues ita my sons 12my fiesta diesel.

charge the battery with ctek charger, but next morning it’s sluggish to start even in this temps.

so, start it with battery starter and it starts. Battery showing 12.3 going in when running, 11 ish when left.

after starting with battery starter, you can then start the car, but it’s sluggish to turn over 

new battery fitted a couple of months ago and does keep a charge.

could this be a starter motor issue? Or solenoid?

12.3 volts seems a bit low when running? Nothing turned on. 

Many thanks for any ideas

 

It's not a starter issue, your battery voltage is way to low.

12.3v is at the lower end of what you'd expect after leaving the car for a few days, nevermind when running! You should be around 14v+ when the engines running, even with a load applied (radio, fan, lights etc.).

I'm surprised the engine turns over when at 11v tbh. Like I say, you should be at around 12.5v.

What's the battery voltage when you've charged it up overnight, before you put it back in the car?

It seems to me like you've got an issue with the car charging the battery, quite likely to be the alternator.

As above it should be nearer 14v when it's running.

I suspect alternator .. if it was winter I'd said maybe battery not holding a charge but in this heat...

 

Did you reset the BMS after you changed the battery so that the charging system knows the car has a new battery?