charging battery in car or disconnect ?

Im about to give my car a day long trickle charge, as it wants to take 6 amps im guessing its either dead or dyeing or flat ! Do you need to disconnect the battery from the car when charging or can you simply connect the charger up to terminals in situ ? thanks

You should ideally remove the -ve terminal connector. If you do this, first put key in ignition to position 1, to disable alarm. You will know if you have not done this correctly as you will be deaf, and possibly concussed on the underside of the bonnet. Low current/trickle charge/conditioners can be attached whilst battery is still connected to car. Ideally leave bonnet open to prevent build up of poisonous and explosive gases.

GT4 you are a wealth of knowledge for that I am thankfull OK so ive done as per your msg, no alrms, and nicely trickle charging now, Im concerned its taking 6mah of charge from the trickle charger, does that indicate 1. batterys shot, or 2.batterys flat or 3. both ? I have priced up a VARTA high capacity battery for 911 ( 996) 86 pounds delivered, didnt want to trust a halfrauds special ! thanks

Varta is a rebadged Bosch, but cheaper. 315*175*175 mm 85 Ah and 800 CCA FIVE year warrany Varta Silver 585 200 080 (short code F18) = Bosch Silver 0092 S5 010 (short code S5 010) Go to somewhere like ManBat = approx £80 http://www.manbat.co.uk/ The 6 mA (0.006A) doesn't sound particularly high. Without knowing the specs/output parameters of the charger in question I do not know if that is the expected/high/low output. If your current battery has seen 3-5 years service (dependent on load/conditions) it may have had it's chips.

Moss Your original post said 6 amps, then your subsequent post says "6 mah". If that means 6mA (6 milliamps) then that's a trickle charge and no great shakes. If your battery is actually drawing 6A of charging current, then a) you must have a pretty hefty charger, b) probably something is wrong with the battery, and c) I'd be standing well back!! By the way, the Halfords HCB096 has worked pretty good for me, and it comes with a 4 year guarantee. Cost me £98 eighteen months ago. On the other hand GT4 knows his onions and his recommendation is higher spec. If you can get it for that price then crack on say I. Cheers H

Sorry I meant 6amps its taking allthough its fallen to 4amps over the past couple of hrs, and i cant find a date code on it, allthough this cars 9 yrs old with full porsche service history i dont know if it has been changed..

Yikes! Then it was pretty well discharged i reckon. I'd change the battery I think - for £100 its not worth the aggro of being let down away from base (trust me - I was that man trying to connect jump leads from a beaten up 110 Landrover to my battery without a major drama whilst several bystanders enjoyed a good laugh!)

I work abroad for 4 months at a time and use a $24.99 trickle charger on my C4 whilst I'm away with no problems. The battery stays connected in situ and always starts first time with no problems!! :thumbs:

A discharged battery has a lower resistance so draws more current, as it charges up the resistance increases and the current consumed drops considerably.

It is probably easier to consider the voltage differential as defining the current "drain" (more of a "push" than a "pull"). At fully discharged, even a trickle charger will "push" the electrons with a potential of 14+ volts. The voltage MUST exceed the nominal 14V a fully charged lead acid electro-chemical configuration is capable of reacting at. The electrons are forced the "wrong way" into the battery (opposite to discharge direction). Only 14+V at almost fully charged will allow electrons to just push in for the final charge. (say 14.1>13.9). However, the differential in a state of "total discharge" is say 14.1 > 0.1. So V=IR, or I = V/R The higher current "push" at initial charge is due to the higher potential difference. As the potential difference drops (as battery charges and charger output stays the same voltage), the current drops.

:bow: your the man GT4 many thanks..

LOL GT4 Its a spin doctor you should be. The days of the unregulated charger and associated battery gassing problems are long gone. Modern battery chargers take full control of the charging rate by altering the supply voltage to the battery cells. In this way battery gassing is eliminated completely. The issues that are relevant in the case of charging a lead acid accumulator are- Energy- joules (J), Charge -Coulombs (Q), Potential difference (V) Volts and Current- Amps (I) One joule of energy is gained by each coulomb of charge when moved through a potential difference of one volt. Potential difference V may be represented by the equation V = E/Q, where E is the electrical energy converted in joules and Q is the charge in coulombs. Chemical energy from a battery is converted to electrical energy in a circuit, this energy being given by rearranging the above formula: E = Q à— V. In reality the current limiting factor and hence the rate of charge of the battery is controlled by the supply voltage which is varied by the voltage regulator in the case of when the engine is running and by electronic circuitry in the case of the modern charger. Anything above 2.15 volts per cell will charge a lead acid battery, this is the voltage of the basic chemistry. However, most of the time a higher voltage is used because it forces the charging reaction at a higher rate. You mentioned gassing GT4, but this is no longer an issue for the modern battery charger because the electronic circuitry limits the charging voltage to below the gassing voltage, which limits how high the voltage can go before undesirable chemical reactions take place. The typical charging voltage is between 2.15 volts per cell (12.9 volts for a 6 cell battery) and 2.35 volts per cell (14.1 volts for a 6 cell battery). These voltages are appropriate to apply to a fully charged battery without damage. If the battery is not charged you can use much higher voltages without damage because the charging reaction occur first.

I don't dispute* the limiting factor (and underlying cause for potential difference). However, your explanation doesn't actually define the current characteristics. ----------------------------------------------------------------------------------- * mathematically I can't: Q = It (current x time) E = Pt (power x time) P = I^2R So from E = QV Pt = ItV P = IV I^2R = IV IR = V V = IR !

Hi GT4, While I agree with your reasoning above you have confined your thinking to electrical terms only. You have introduced electrical resistance which could be used to explain how the current falls off as the battery charges. (making the assumption that as the battery charges the resistance increases and so current falls) .. I =V/R The thing is though, we are dealing with an electro chemical system in which the charging brings about chemical changes to reconstitute the chemical compounds. There are many variables which makes things "not linear" eg temperature changes, acid strength etc. As a battery charges these chemical changes do influence the charge current but not according to Ohms law. Because of this you cannot rely on electrical formulae to describe accurately what is happening. The modern battery "smart" battery charger such as the optimate or C-teck battery chargers alter the charge rate in real time by changing the charging voltage before going into float mode and supplying a tiny charge again by setting the charging voltage. Some of this is discussed here- Charge Termination Once a battery is fully charged, the charging current has to be dissipated somehow. The result is the generation of heat and gasses both of which are bad for batteries. The essence of good charging is to be able to detect when the reconstitution of the active chemicals is complete and to stop the charging process before any damage is done while at all times maintaining the cell temperature within its safe limits. Detecting this cut off point and terminating the charge is critical in preserving battery life. In the simplest of chargers this is when a predetermined upper voltage limit, often called the termination voltage has been reached. This is particularly important with fast chargers where the danger of overcharging is greater. Safe Charging If for any reason there is a risk of over charging the battery, either from errors in determining the cut off point or from abuse this will normally be accompanied by a rise in temperature. Internal fault conditions within the battery or high ambient temperatures can also take a battery beyond its safe operating temperature limits. Elevated temperatures hasten the death of batteries and monitoring the cell temperature is a good way of detecting signs of trouble from a variety of causes. The temperature signal, or a resettable fuse, can be used to turn off or disconnect the charger when danger signs appear to avoid damaging the battery. This simple additional safety precaution is particularly important for high power batteries where the consequences of failure can be both serious and expensive.

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