Batteries

[Gardenshed]

What's the combined wisdom for battery replacement and when replacing, are there any recommended upgrades?

I've got 2x Domestic 120ah 12v batteries and 1x 100ah engine start battery. All lead acid.
Very simple charing from the engine alternator and 1/2/both/off rotary switch
Sterling shore-power charger/maintenance thingy hooked up when on a pontoon

Now 7 years old and probably getting to the end of their lives.

What to use for domestic? standard lead acid, AGM or other tech?

What to use for starting?

Is it worth the expense of moving to lithium ion? There is a creeping increase on board of electric systems. Fridge was an engine driven compressor, now electric, heating installed (hot air) and needs current for the fan, additional chart plotter, more interior lights and charging of electronic stuff, but so far all manageable

Halfords lithium battery starter thingy to use as an emergency engine start / back-up if everything is flat & so far only needed for the Landrover!

[Aja]

Need to tell us how you keep the batteries charged. Do you like running the engine when away from 240v? What size is the alternator? Do you have solar?

I have 3x 130Ah Lead acid batteries being fed by a 60amp alternator and more importantly 180W of solar through a Victron MPPT 15/70 controller. With fridge and heater and led lights I sometimes run the engine in the morning to bring voltage back up but rarely see voltage drop below 12.4V overnight. Unless really cloudy and overcast for a couple of days (not unknown) daytime sun keeps up with all the above usage.

I'm not convinced yet I need to invest in AGM.
100Ah seems over the top for an engine start battery.

As always the above works for me. AJA sits on a mooring.

Hope this helps.

Donald

[Gardenshed]

Thanks for the comments

No solar
Alternator: strapped to the side of a Perkins 4108 so I suspect 60amp
Boat on a pontoon so float charge/maintenance charge when I’m not on board
Switch off fridge etc when sailing and on when the engine is running.
Ok to run the engine for charing if needed and the 100ah just gives extra capacity if i run down the domestics

Agree, not sure what you get from agm for the extra money, compared to a decent sealed lead acid battery

I’m also not sure why it’d be worth moving to lithium. When the price drops to £300 for a 100ah LiPo then it
Might be worth it

[cpedw]

As I understand it (which is not completely) the big plus of AGM is that they can recharge a lot more quickly. So if you want to limit engine hours for charging and the alternator regulates at a modern high-ish voltage (about 14.4V; older regulators are around 13. then AGM might be advantageous.

Lithium will cost a lot but is lighter for given useable capacity and lasts longer. But it's more complex than just replacing the batteries. The charging system needs altering to suit.

7 years is quite old for domestic batteries. Starter batteries tend to last longer IME. Your starter is bigger than needed so should last longer but if you've been using it to help out the domestics, then bets are off.

[marisca]

I do not claim wisdom on this subject but I have just replaced my pair of domestic batteries with 105ah sealed lead acid costing a tad over £100 each. The predecessors were 4 year old but thanks to my stupidity in leaving them connected to the domestic radio for over 2 weeks had been dragged down to zero and while they recovered capacity had definitely suffered and they dropped voltage under load much faster than felt comfortable. My buying decision was predicated on size (size 27 fitted the battery box) and cost, just in case I was stupid again. I have about 140ah available which should keep the instruments, radio and nav lights going for well over 24 hours which I reckon is enough.
So, anyone want a pair of 110ah lead acid that hold 12.9v happily?

[BlowingOldBoots]

It would be a lot less cost to buy some firm of lead a use and upgrade the alternator to force more efficient charging.

I am in the same camp as you but just starting out. Lithium would require a new system to charge, not just so called drop in, far from it.

My view, is that for 5 more years lead acid will do, and by then hopefully lithium tech will be well developed and lower cost. It’s too expensive at the moment.

However, say you decide you want a new alternator, smart regulator, or other such upgrades, research to upgrade for lithium ready stuff, but by lead acids.

I may rip out my old system and replace with new, and I will cost full lithium change over, but back off the fag packet calcs, lead acid is lower cost, even with new alternator.

A big advantage of lithium is weight and volume savings. If space is important, you can free up a lot of space. For example, your house bank can probably be replaced by a lithium battery set the size of a shoe box, and have more useful capacity by a country mile.

[Burst Boiler]

It would be a lot less cost to buy some firm of lead a use and upgrade the alternator to force more efficient charging.

This is the correct answer. BUT. You might find (as i did) that the ultimate limit is how much current the batteries can accept. Very rough rule of thumb is 10%, in the sense that 200Ah of capacity will accept 20A max current. I do hear tales of people upgrading from 60A alternator to 100A and not finding any improvement - the alternator current isn't the issue. Smarter regulator (eg battery voltage sensing, choosing the right settings for shore charger) or other improvements like low-loss diode splitter certainly help, but usually only once the batteries are up above 80% charge, forcing in the last bit, which takes a while since current is lower by then. After extensive research, I concluded that the dumb answer (bigger batteries) was the solution - not so much for the capacity itself, but for the greater charge acceptance. AGMs help here since the rule of thumb is maybe 15% acceptance. In general use, my batteries probably cycle in the 50%-80% charge state. Its difficult(time consuming) to get them above 80% when cruising. Sobering to think usable capacity in practice is only about 30% of the sticker value.

[BlowingOldBoots]

Note: “firm of lead a use”, should read form of lead acid …

Old eyes, tired eyes, small phone keyboard excuses!

[Gardenshed]

Sobering to think usable capacity in practice is only about 30% of the sticker value"

that's one area where LiPo give a real benefit, i.e. that you can deep discharge them and get much more benefit from all the aH that you've installed

[Gardenshed]

Am I right in thinking that a lead acid battery has approx 50% DoD (depth of discharge) so in reality, a 120aH battery can supply 60aH
Lithium batteries have 90% DoD so a 67aH lithium has approx the same effective capacity as a 120aH lead acid one

so to do a like for like price comparison, I shouldn't be comparing a 120aH lead acid/Gel/AGM battery with a 120aH lithium one

[Burst Boiler]

Exactly. Leads shouldn't (routinely) go below 50% without shortening their life. As I mentioned, getting them above 80% generally needs a long time with a good charger (meaning effectively shore power) and above 90% not really practical or possible unless they are brand new. So you might say 33% instead of 50% and compare 120Ah lithium with 320Ah lead.

[SteveN]

I'm afloat for the winter in a marina without power (although in extremis I could run several extension leads to a 6A shore supply) so I decided to go for a portable lithium solution. I bought a 30Ah Lifepo4 battery which weighs 3Kg and equipped it and the boat with quick release Anderson (50A rated) connectors. I charge the battery at home, pop it into my cycle backpack and connect it up once there. It'll run diesel heater, lights, TV, instruments to warm them up etc. for a full day and evening on the boat, then take it home and charge it up again. 100% of the 30Ah is usable - I've tested it down to BMS shut-off.
It's been a revelation, particularly the way that voltage is maintained across its capacity (which the diesel heater is very happy about), and I suspect that I'll continue to use it once back into summer sailing.
Lead-acid seems very antiquated once you've wet your feet with Lifepo4.

[marisca]

Obviously, I'm now suffering buyer's remorse - having spent over £200 and hoiked the not unconsiderable weight of 2x105ah up into my boat I'm questioning my sanity. If only I'd waited for this thread to point out the error of my ways. Ah well, in about 5 years or so, if I'm spared, I'll get another chance to make an arse of it.

[Burst Boiler]

Yeah, you should have bought 3x105Ah old type lead acids.

[NorthUp2]

One point to bear in mind with LiPo is that they do not like temperature extremes- a steel boat on the Caley canal had issues during the cold spell in December.
Below 5deg C victron lithium batteries shut themselves down, both for charging and supplying power to the boat, and if you're charging on shore power the charger/ inverter also shuts down because it thinks the batteries have been disconnected... cold dead ship when you go aboard!
There's more- the internal monitoring electronics built into the batteries continue to discharge the batteries at just under an amp, so after 10 to 14 days the bank is at zero on the gauge and probably will not recover.
The answer for us is a 300 watt tube heater , 240v, on the shore power with a thermostat. Not failsafe, but we'll add remote monitoring...soon

If you have a 24v system, once warmed up (both you and the batteries) you then spend a day or two balancing the battery voltages to within 5 percent of each other before charging at full current, or risk more cell damage