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Use and Care of Batteries

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USE AND CARE OF BATTERIES. (Author = Safariboy)

Batteries seem to produce a great deal of correspondence on the forum.
The first thing to remember is that a battery is a convenient source of energy but the amount that it can store is limited. A 100 A-Hr battery can be expected to give about 0.5 to 1 kW-Hr of energy before needing to be recharged. For comparison an EHU will give you that in less than 20 Min. and a 6kg propane bottle will give about 85 kW-Hr. At home 1 kW-Hr of electricity costs about 10p and of gas about 3.5p.
Battery power is convenient and portable but limited.
A battery should last many years if looked after.
Rule 1 When using a battery aim not to discharge to less than 50% of its capacity. 10% is the absolute maximum but do that too often and with most batteries you will need a new one.
Rule 2 Recharge as soon as possible after discharging. A discharged battery will stop working after a few days.

Types of battery. All motor home batteries at the moment are lead/acid. There are different types. The first division is leisure batteries that are designed for relatively small currents supplied for several hours and starter batteries that are designed to give a large current for a short time. Make sure that your supplier knows which you need.
The second division is between gel or sealed batteries and wet acid batteries. Gel batteries have the liquid thickened with a jelly so they cannot spill. They are also sealed so hydrogen and oxygen do not escape but will recombine. There is a safety relief valve so ventilation is still required.
The electrical requirements of Gel and wet acid batteries are slightly different and so your charger will need to be set correctly. Adding extra batteries is not covered by this entry but if you do the two batteries must be of the same type and age.

Battery charging is usually automatic on modern motor homes. When the engine is running a relay connects the engine battery to the leisure battery and both charge together. The leisure battery will charge quite slowly and if you have been on an aire the night before and discharged the battery to 50% it will take several hours to charge the battery fully. In practice it is unlikely to get to full charge this way anyway.
If your van is in storage a 15 minute run will not be enough to restore the battery.

How do I know the charge left in my battery? The only property that is easy to measure is the voltage. There are other systems but they are not common and quite expensive. Most motor homes come equipped with a voltmeter. Unfortunately the voltage only changes slightly when the battery is charged up. (Roughly 11.8 - 13.V) and changes in temperature will also change the indicated voltage. When charging the indicated voltage will be higher; Usually 13.8V. To find the charge use this approximate rule. All voltages measured after leaving the battery off charge for about 1 hour and refer to a liquid battery. For gel batteries the voltages are a little lower..
(1) Less that 12V less than 50% charge. Requires recharging urgently.
(2) 12-13V partly charged. At 12.5V the battery is probably nearly 80% charged.
(3) Above 13V over 90% charged with 13.2 being the voltage at which gassing has started and the charging current will split up water rather than add extra charge to the battery. (This limit is 14.4V measured when the battery is charging)
(4) It is possible to charge to a slightly higher voltage and this gives a little more capacity but this requires special monitoring.
Most modern motor homes have a multiple stage EHU charger which charges near the optimum depending on the state of charge.
Your van may have a built in charge meter but this will only give a very approximate reading as it is essentially a voltmeter.

When on EHU you can usually charge either battery by a switch on the control panel. There are vans where this is not possible and the control panel switch only changes which battery is discharged. Be careful that you do not use the engine battery when you are not on charge or you may not be able to start the engine! (It is the same switch)
Most modern battery chargers will not overcharge the battery if you leave them on when the battery is in storage BUT this may not be true of yours so ask your manufacturer for advice on this point.

Will your battery discharge in storage?
If your battery is in good condition and fully charged it should remain in good condition for some months if there is no discharge. Unfortunately many modern vans discharge the engine battery all the time even when all is turned off. This current is about 0.1 to 0.2A
There are two ways of dealing with this.
(1) Leave the van connected to an EHU all the time or for a few hours a week. A solar panel would also work but you will need one rated at about 20W.
(2) Disconnect the earth lead of the engine battery. This will turn off any security system that you have and may make it difficult to lock the doors.

Topping up
When a battery is being charged some of the water in the sulphuric acid can be split into hydrogen and oxygen. This mixture is explosive and so any battery compartment needs to be well vented.
The water needs replacing with pure (distilled) water. Do not over fill. Just over the plates is correct. If you check about once month you will soon find out how much your system uses. Do not add battery acid or any water not specified for topping up. If you battery does not require topping up that is quite normal. If it requires topping up all the time the charger may require adjustment.
A few calculations
The capacity of a battery is measured in A-Hr. If the current from the battery is one amp you will remove 1 A-Hr each hour. (So a 1.5A lamp used for 10 hours will use 1.5 x 10 = 15A-Hr)

If you use an inverter you need to remember that the battery current will be at least 20x the current produced at 240V. The result is that a 500W appliance (a hair dryer for example) will require about 45A from the battery. At this current the capacity of the battery will be less than expected and although it will work you will need to recharge frequently. You will also require heavy short wires between the battery and the inverter. (See the section on inverters)

If you are camping without EHU a great deal consider changing the lamp bulbs to LED types. The current consumption will be very much less.
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