I have a 2000 BMW E46 323i. I planned on not driving my car for several weeks. I have one of those solar panel battery rechargers. It generates electricity via solar power, then has two alligator clips to connect to the battery. This way, it recharges the battery in a constant electrical power, but not at high volt level as a jump start.

I used it on my other car and as long as I parked my car in my driveway (under the sun), it recharged the battery of the car.

I parked the BMW outside and put the solar panel recharger on the windshield, then connected the clips to the electrical connectors in the engine compartment. For this BMW, the battery is in the trunk. There are two connectors, the negative and positive connectors, in the engine compartment. These connectors are connected to the battery in the rear.

These connectors are to be used for a jump start. The BMW user guide says to use these connectors if the BMW's battery is dead. So I am assuming that I can use these two connectors to recharge the battery.

However, it doesn't seem like the battery is being recharged via these connectors. I have a multimeter and measured the battery before I connected the solar panel recharger. It measured 12.20Vs. Then a week later (today), I measured the battery again with the multimeter. It now measures 11.33Vs. It doesn't look like the battery is being recharged.

It can't be the solar panel because it works on my other car.

The two connectors in the engine compartment can be used to jump start the BMW. But can I recharge, not jump start, the battery using these two connectors ?

You can charge via the cigarette lighter. Maybe try that.

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You can charge via the cigarette lighter. Maybe try that.

Is the BMW cigarette lighter port an open connection? In other words, if I take the key out of the ignition, can the cigarette port still draw power? My other car's cigarette lighter is not an open connection. You take out the keys and the connection is cut. No power in or out of that connection in my other car.

 

Yes, the jumper posts under the hood can be used for charging, same as the battery terminals.

Know that 12.2V is only about 60% charged, and 11.33V is dead as a doornail.

Those solar “chargers” put out very low current, and are only useful as a “trickle charger” to maintain battery voltage against normal self discharge.
Get a real battery charger that provides at least 6A (preferable 10A) and charge it overnight on that.

Your E46 is likely draining the battery due to a parasitic current drain, from aftermarket stuff like audio, DICE media player, lighting, etc., or one of the common drains like electric engine fan, final stage resistor, etc.

 

Those solar “chargers” put out very low current, and are only useful as a “trickle charger” to maintain battery voltage against normal self discharge. Get a real battery charger that provides at least 6A (preferable 10A) and charge it overnight.

^^^this. Get a Ctek MUS 4.3 (they make the BMW branded charger for our cars) with the adapter that plugs into the lighter and mount it on the wall of your garage. Plug in, leave the window cracked for the cable to pass thru, and lock the doors. Done. Also allows you to check voltage without opening or unlocking the car thru the cable.

 

I'm with Bali. The mere fact that you have a solar trickle charger is a sign your E46 is problematic when it sits. I left mine for 4 weeks over Christmas in a cold northern climate in an unheated garage and it started instantly with no discernible difference from the instant start if I'd driven it an hour ago. Ironically, I was going to put one of my trickle chargers on it while we were away and because of the trunk battery I gave up and didn't install it. I didn't even think of using the underhood connection as you did! Anyhow something's amiss in your E46 it seems. A good auto electrician can quickly track these parasitic losses. There is a specific procedure and it's worth paying someone an hour of shop time to track it.

 

If your test meter has a 10A function you can do the test yourself. BTW, how old is the battery?

 

Unfortunately, the multimeter doesn't have a 10A function. The battery is about 6 years old.

 

I recharge my battery using the battery terminals under the hood at the drug bin. My battery charger is a 2/6 amp Schumacher. I usually just use the lower 2 amp setting and it works fine. Recharges the battery very well. What amperage is your solar charger?

 

The package says 0.2 amps. Not even close to 2 amps. This is a trickle charger. I have a jump-starter charger too (the ones with the big lead battery and two battery clips that you can jump-start any cars).

 

There may be a power drain larger than the amount of electricity the solar charger is providing. So you still have a net loss of charge. IIRC, the draw on the battery should be under 100mA with the engine off and the electronics in "sleep mode".

As mentioned above, charging via the jump-start posts should be fine. I use a 2 Amp battery maintainer connected to those posts, works great.

 

I use a solar charger more to compensate for normal parasitic draw over a period of inactivity. But I too have left a car for over a month and had it start.

 

Any recommendations on good solar chargers?

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Subbed because I am curious about this

 

6 yrs and down to 11.3v.....it's toast. I see a new battery in your future.

 

I go along with some of the other suggestions that your car has a parasitic draw. Ultimately the fix for your main issue lies there.
Your battery is also past the shelf life date. Replace it.

I have this great customer. She absolutely loves her 1999 528i Touring. (M52TU) 325K miles and we installed a factory engine because she cooked the old one @ 265K.
She very often goes away on business trips for 2 weeks at a time. Every 3rd. or 4th. time she comes home the battery is completely flat. Battery 3X, alternator twice, checked for closed current violation (multiple days) several times, nothing. Threw parts at it (god I hate that) of aux fan, Ign. switch FSR disconnected Nav. etc. etc. It's embarrassing.

To that end we have found an amicable solution of a solar charger, very similar to the one above. Sits on the dash and plugs into the cigarette lighter. Gets the job done.

 

I'm shocked you never found the drain.

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Babaloogats,
You have two problems. 1. Your battery is near death. 2. You have a parasitic draw. Just as MrMCar stated.
If you are really lucky you might be able to re-charge the battery. Suggest you take the battery to an Auto Parts store and have it checked. If good put a good charge into it. If bad get a new battery on the spot. Then start checking for that parasitic draw. It won't go away by itself. One way to check if you are getting parasitic draw would be to install a fully charged battery, check the voltage, then 24 hours later check it again. Assuming you do not drive the car. Would expect very little drop in voltage unless you have some type of parasitic draw.

 

Perform a parasitic draw test. Super simple. Normal parasitic draw on the e46 is .04 amps. I just did this on my e46 after my door actuator was causing an intermittent parasitic draw.

Also, make sure you perform the test after 16-20 minutes. Which is how long it takes the e46 to fully enter sleep mode. Be sure you have nothing else on (dome lights, trunk lights, etc.)

I'm currently milking a 7 year old battery. She only holds 12.4 volts (50% capacity). Unfortunately the AGM Battery I want isn't in stock.

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I'd be getting a new battery first. Then, as suggested above, see how it makes out over 24 hrs. Or try the test for fun. I've had older batteries that would charge up to mid 12s, but then start slowly dropping (disconnected).

 

This is what you should be seeing at idle with no auxhilaries switched on. This is your objective if you want a healthy electrical system.

 

If you drive your vehicle once a week or less and you have a garage get a Deltran Battery Tender. I've had one for years and I use it a lot.