New member - battery issue.


After 20 years with a company cay I now don’t have one so got myself a MX5.  It’s been standing around a bit so the battery is a bit weak.


Question;  Is it ok to attach the charger to the battery without disconnecting it?  And if I disconnect it will the car loose its settings?  Windows (ECU?) etc?


Thanks in advance,




Hi Steve

Would be useful to know what MK of MX5 you have Steve as slightly different advice but…

OK to connect charger to battery whilst attached to car(MK1 - MK3) - use a smart charger.

The MK3 will loose radio/engine settings if disconnected - take 20 mins or so of driving to completely relearn. No effect on engine for MK1 - MK2 but may be an effect on radio, depending on what you have fitted.


Depends on the charger.

Even a low capacity charger of poor design could have a high unloaded voltage and spike the electrics momentarily.  So if it’s a 30 year old item of unknown provenance, no.  

A friend of mine has an old commercial ‘booster’ trolley that probably cost a fair bit of money in its day.  I have measured the unconnected voltage at over 17 so I wouldn’t let it near my cars!

On the other hand I have used a CTEK MXS 3.8 on a Mk2 and now a Mk4 without disconnecting, and without problems (it’s what it is designed for).