What do the numbers on a battery mean

[Blueboy]

Hi all I don’t know anything about batteries. I need to run the phone charger, music and lighting for c two / three days wild camping off grid.
I've had a look and can see my main battery and leisure battery are both AGM Varta 7 po 915 105 a 12v 75ah 420
What the heck does all that mean. Is this good or not good? I know it’s got the OEM split relay. I’m going to get a DC to DC but do I need to upgrade either battery or do those letters mean they’re enough?

 

[Pete C]

Got a photo ?

Pete

 

[Blueboy]

Got a photo ?

Pete

Got a photo ?

Pete

 

[Dellmassive]

Got a pic of the other battery?

Under the seat.?

 

[Pauly]

7P0915105a is the part number
75ah is the capacity of the battery
420a and or 800a is the output rating of the battery, not sure what’s what with these but often referred to as CCA or cold cranking amps and it’s an indication of how juice it can bang out to crank an engine
Engine battery is fine and can be left alone, the leisure battery can be swapped for a larger capacity unit if required but that’s only if you need more capacity

 

[Blueboy]

Cheers Pauly, really appreciated, what’s the spectrum I’m looking at - I mean where does 75ah fit in capacity wise - so if I wanted to up it what are my options?

 

[Ads_Essex]

..where does 75ah fit in capacity wise..

I have an Xtreme 110Ah AGM under my drivers’ seat. I think there’s a 120Ah available, but maybe not much more.

You could go crazy and get yourself a lithium battery. Big money but big power.

 

[Pauly]

It’s all down to space, you can go upto around 100-110ah

 

[Phil_G]

I need to run the phone charger, music and lighting for c two / three days wild camping off grid.

None of those things are high drain, a phone charger uses next to nothing, 'music' could be your van radio (2 or 3 amps not too loud) or a rechargeable MP3 player (next to nowt again) and lighting - led lights are usually around a watt each, thats an amp for 12 of them assuming they're switchmode. You'd have them on maybe 4 hours max? 4Ah.
Your van radio, guess 3A for 4 hours, 12Ah. Phone, MP3 charge, an amp in total, for as long as it takes to charge, say 5Ah. Guesstimated total 21Ah
You should only ever take half of the 75Ah capacity from the battery, so with everything in use as above you've at least two days worth, but thats a conservative guess, you'd probably get three in practice. Three days is only 2 nights with the lights on! All very 'finger in the air', 'your mileage may vary' etc
A cheap panel on the roof, or a 'suitcase' panel would extend this indefinitely. No need to spend megabucks

 

[Blueboy]

Thanks guys, I’m wishing I paid more attention in physics 40 years ago now

 

[Blueboy]

None of those things are high drain, a phone charger uses next to nothing, 'music' could be your van radio (2 or 3 amps not too loud) or a rechargeable MP3 player (next to nowt again) and lighting - led lights are usually around a watt each, thats an amp for 12 of them assuming they're switchmode. You'd have them on maybe 4 hours max? 4Ah.
Your van radio, guess 3A for 4 hours, 12Ah. Phone, MP3 charge, an amp in total, for as long as it takes to charge, say 5Ah. Guesstimated total 21Ah
You should only ever take half of the 75Ah capacity from the battery, so with everything in use as above you've at least two days worth, but thats a conservative guess, you'd probably get three in practice. All very 'finger in the air', 'your mileage may vary' etc

Phil if I were to run a Webasto for a couple of hours that would probably change things I’m guessing - what amount of Ah per hour do you think this might use?

 

[rover220]

Webasto for a couple of hours not ideal. They can draw around 10a when firing up dropping to around 1a

 

[Phil_G]

Its only high current whilst igniting, thereafter its just the fan and the pump.
But you're adding things as you think about it more, so I would suggest that a panel solves all your problems, then you dont have to worry about it. I dont think a bigger battery is the answer, even a 120 (60 usable) is only 50% more than you have, its not even double, it stretches 2 nights to 3, thats all, for a similar cost to a panel which would remove the limit altogether

 

[Blueboy]

Its only high current whilst igniting, thereafter its just the fan and the pump.
But you're adding things as you think about it more, so I would suggest that a panel solves all your problems, then you dont have to worry about it. I dont think a bigger battery is the answer, even a 120 (60 usable) is only 50% more than you have, its not even double, it stretches 2 nights to 3, thats all, for a similar cost to a panel which would remove the limit altogether View attachment 71283

So leave the batteries as they are but add a solar unit? I had thought of that but thought changing the battery would be simpler
If I left the batteries, and added a panel would I need the dc to dc or wouldn’t there be much point in adding this if I’m topping up every day from the panel?

 

[Phil_G]

If we're still talking about a weekend camp off grid, you dont need a B2B, presumably you wont be driving so a B2B wouldnt be doing anything.
If you dont want anything permanent, get a budget suitcase panel. Some come with the controller, some dont but a cheap Chinese PWM will suffice,
I've used several of these generic controllers, all perfectly ok: 10/20/30A USB Solar Panel Battery Regulator Charge Intelligent Controller nw | eBay
Just connect it to your leisure battery with croc-clips when you set up camp. If this is going to be a regular thing, I'd fit a roof panel, its easy peasy, fit & forget.
Here's one example, £110 for a complete kit, 100W panel and a controller: 30/50/100w Flexible Solar Panel PV Photo-voltaic Boat Marine Caravan Home Flexi | eBay
Its just a suggestion, I dont think a slightly bigger battery will solve your problem - what if your break runs to 4 days?
Cheers
Phil

 

[Blueboy]

If we're still talking about a weekend camp off grid, you dont need a B2B, presumably you wont be driving so a B2B wouldnt be doing anything.
If you dont want anything permanent, get a budget suitcase panel. Some come with the controller, some dont but a cheap Chinese PWM will suffice,
I've used several of these generic controllers, all perfectly ok: 10/20/30A USB Solar Panel Battery Regulator Charge Intelligent Controller nw | eBay
Just connect it to your leisure battery with croc-clips when you set up camp. If this is going to be a regular thing, I'd fit a roof panel, its easy peasy, fit & forget.
Here's one example, £110 for a complete kit, 100W panel and a controller: 30/50/100w Flexible Solar Panel PV Photo-voltaic Boat Marine Caravan Home Flexi | eBay
Its just a suggestion, I dont think a slightly bigger battery will solve your problem - what if your break runs to 4 days?
Cheers
Phil

Cheers Phil, really appreciated