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I need to charge my battery, do I need to disconnect the terminals whilst the charger is doing its work?

Many thanks.

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From my handbook

"Before recharging
When recharging, the 12-volt battery produces hydrogen gas which is flammable and
explosive. Therefore, observe the following precautions before recharging:
● If recharging with the 12-volt battery installed on the vehicle, be sure to disconnect the
ground cable.
● Make sure the power switch on the charger is off when connecting and disconnecting
the charger cables to the 12-volt battery."

Have to ask, why do you need to recharge the battery, how has it become discharged?

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If you disconnect the ground cable what systems do you lose and has anything to be reset when reconnected? I will be taking my car off the road for 3 months this winter and was going to connect a maintenance charger during this period. However I intend to ask for advice from the Lexus Service Dept nearer the time.

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Thank you for that Peter, much appreciated. 

Not sure why it has discharged.  It could be that I left the dashcam on all day and night.  Normally if I go out the dashcam continues to record whilst I am parked up but when I get home and put the car on the drive I usually disconnect it completely.  I thought that I had the 'park' setting set to automatically switch off after 6 hours or when the battery gets down to 11.4 volts.  I need to check this when the battery is charged up again.

Do you have any idea how long a Home DIY type charger would normally take to recharge a 12v battery?

Thanks again for the help given.

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You need to know the normal charge rate of your charger "not the maximum output", and the battery capacity marked on the battery in AH. Typically most chargers charge at around 4 amps. So if you battery capacity is 45ah "amp hours" you divide this by 4 "the output of the charger" then add 10% for the inefficiency of charging. = 45 divided by 4 = 11.25 plus 10% = 12.375 hrs. So somewhere around 12 hours. If your battery is 60ah about 17 hours.

These calculations are based on the battery being fully discharged.

John

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I've only ever used a 'smart' charger on my Mercedes, the CTEK MXS5. I had a permanent quick connection installed (MB use the same chargers and supply the connection kit) and always charged with the battery installed and connected. 

The CTEK automatically tests the battery and varies the charge rate as needed. I often left the charger connected for 3-4 days or just overnight if I needed the car. Battery showed fully charged according to the display on the CTEK.

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2 hours ago, NemesisUK said:

I've only ever used a 'smart' charger on my Mercedes, the CTEK MXS5. I had a permanent quick connection installed (MB use the same chargers and supply the connection kit) and always charged with the battery installed and connected. 

The CTEK automatically tests the battery and varies the charge rate as needed. I often left the charger connected for 3-4 days or just overnight if I needed the car. Battery showed fully charged according to the display on the CTEK.

 

Thank you for your input NemesisUK.

Will any of he CTEK chargers be suitable for use with my 300h? Can you explain a little more re your 'Permanent quick connection' please.

 

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The permanent connection is simply leads attached to the battery terminals that end in a simple socket that the charge cables from the CTEK plug into. One can have that socket conveniently positioned so making it easy to attach the CTEK without having to access the battery.

I'd say the CTEK MXS5  would be fine for the 300h. The CTEK has a very low ripple current, so shouldn't adversely affect vehicle electronics but I would take expert advice from Lexus regarding keeping the battery earth connected whilst charging. 

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