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  • Battery questions

    Hello all. Tried to drive the car today but battery completely dead - not even enough power to unlock the doors. I use a solar powered trickle charger which plugs into the cig lighter. Usually works a treat but seems to be an issue with either the charger or the socket. Anyhow, I got the boot open and clambered in to pull the bonnet lever. But the bonnet won't open. Locked, or unlucky coincidence? I am not sure.

    I figure no problem and I will just jump start it direct from the battery in the boot but I remember there are special jump terminals under the bonnet and a set procedure in the manual. Is it a bad idea to try it direct to battery? Should I remove the battery and charge it in the house? Or is there another way to get the bonnet open? All thoughts and advice welcome!

  • #2
    Well the battery is the real source of power for the car, so there is no reason you can't connect direct to the terminals to jump start the battery. The terminals under the bonnet just make it easier.

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    • #3
      A CTEK battery charger is a great investment
      Not actually in the least bit fat

      2000 S50 Titanium Silver / Black
      ACS Suspension, Exhaust & Type III Wheels
      Simota carbon air intake | Strong Strut Front Brace

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      • #4
        Originally posted by c_w View Post
        Well the battery is the real source of power for the car, so there is no reason you can't connect direct to the terminals to jump start the battery. The terminals under the bonnet just make it easier.
        That's not strictly true - the terminals under the bonnet are there for a reason. Although it's a negative earth circuit, strictly speaking you shouldn't connect the earth jump lead to the negative terminal of the battery. Don't get me wrong, I'm sure we've all been doing it directly to the battery for years without issue but it's not best practice as there is a risk you can damage the battery so it will no longer recharge and in extreme circumstances could cause an explosion (depending on the condition of the duff battery and its acid or gas content). The risk is small along the same lines as causing an explosion by smoking while filling your car with petrol - highly unlikely, but the risk still stands. If you insist on using the battery's positive terminal, you should NOT use the negative terminal but connect the earth lead to a good earth elsewhere (which is handily provided in the engine bay, along with a handy positive terminal too).

        Depending on the condition of your battery, there's also a risk of frying your ECU by connecting an additional battery / 12volt supply to your existing battery. Funnily enough one of the Porsche guys has recently fried his 911 ECU by doing exactly that, although I think he connected the leads the wrong way round first (Porsche uses black leads for both battery terminals, so another reason to use the engine bay terminals which should make it fool proof!!)
        S54 Black / Imola. S50 Titan / Black. And some bits from Stuttgart.

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        • #5
          Also worth noting that the stuck bonnet is not due to flat battery. Have you tried getting a friend to lean on it at the front whilst you pull the release?
          1998 ///M Coupe

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          • #6
            I would charge the battery just to be safe, I think you can get access to the bonnet catches from below if they or the cables have failed.

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            • #7
              Leave the battery itself on trickle maybe, or connect to another car idling for a few minutes, then go for the jump.

              This helps to minimise surges/builds that battery up slowly/brings systems to life sympathetically.

              If you were really worried several companies sell a surge capacitor type thing to guard against spikes.

              Safest is to charge it slowly then try...

              A lot of scaremongering but In reality I'm sure it will be fine as long as you are sensible.

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              • #8
                Originally posted by PJ Westerby View Post
                That's not strictly true - the terminals under the bonnet are there for a reason. Although it's a negative earth circuit, strictly speaking you shouldn't connect the earth jump lead to the negative terminal of the battery. Don't get me wrong, I'm sure we've all been doing it directly to the battery for years without issue but it's not best practice as there is a risk you can damage the battery so it will no longer recharge and in extreme circumstances could cause an explosion (depending on the condition of the duff battery and its acid or gas content). The risk is small along the same lines as causing an explosion by smoking while filling your car with petrol - highly unlikely, but the risk still stands. If you insist on using the battery's positive terminal, you should NOT use the negative terminal but connect the earth lead to a good earth elsewhere (which is handily provided in the engine bay, along with a handy positive terminal too).

                Depending on the condition of your battery, there's also a risk of frying your ECU by connecting an additional battery / 12volt supply to your existing battery. Funnily enough one of the Porsche guys has recently fried his 911 ECU by doing exactly that, although I think he connected the leads the wrong way round first (Porsche uses black leads for both battery terminals, so another reason to use the engine bay terminals which should make it fool proof!!)
                Are you suggesting it's bad practice just to jump from the bonnet terminals, or to use them for anything - such as trickle charging? Mine sits on a CTEK connected there most of hte time.
                S54 Seca Blue - ACS Short shift and Exhaust. Luverly.

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                • #9
                  Thanks very much for the advice. I've done the responsible thing and bought a charger. Bonnet catch is the next challenge but leaning on it sounds a good first option!

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                  • #10
                    Originally posted by Seca Blue View Post
                    Are you suggesting it's bad practice just to jump from the bonnet terminals, or to use them for anything - such as trickle charging? Mine sits on a CTEK connected there most of hte time.
                    Not sure if you've mis-interpreted my post - it's not bad practice but BEST practice to jump using the under-bonnet terminals NOT direct to the battery.

                    A decent trickle charger / battery monitor should be fine using either the engine bay terminals or directly to the battery and a CTEK is generally fool proof and you can do pretty much anything with them without causing problems (reverse connections etc). I have four of them (two direct to battery terminals, and two via the comfort connect 12v socket in the cars). I have previously clipped them to the engine bay terminals too.
                    S54 Black / Imola. S50 Titan / Black. And some bits from Stuttgart.

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                    • #11
                      Ahhh gottcha - ta.
                      S54 Seca Blue - ACS Short shift and Exhaust. Luverly.

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                      • #12
                        Originally posted by Kuvvux View Post
                        Thanks very much for the advice. I've done the responsible thing and bought a charger. Bonnet catch is the next challenge but leaning on it sounds a good first option!

                        Some more details here regarding bonnet,

                        https://www.zroadster.net/forum/view...elease#p324495

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