Bav 37 Cruiser (2006) Battery Change

[Scorcher IV]

Hi All,
I would appreciate some collective wisdom. Currently I have two Varta 140AH batteries as my house bank, they are at least six years old. Can I replace them with two Varta 180AH batteries without having to change the alternator or the battery charger. Engine is a D2-40.
Regards
Simon

[Rampage]

The change you’re proposing is marginal.  No need to change anything other than the batteries themselves.

[fjoe]

Electrically no problem but check the dimensions (width of the 180Ah is 223mm compared to 189mm of the 140Ah battery)

[PEA-JAY]

F.Y.I. On my 2005 Cruiser 39, two x 180AH do not fit side by side!

[Holger]

If you want to replace the batteries you may consider to install lithium (LiFePo) batteries. They are smaller and the weight (at similar power) is far less. On our 37 Cruiser (2006) we replaced two very heavy 135Ah traditional batteries with two 150h LiFePo batteries. Other than that we did not change anything and to date it works. The 230V charger is usually no problem if you have the charger installed by Bavaria. You need to check the alternator. If your alternator is only an 50A alternator you will likely face problems sooner or later in particular if the batteries are almost empty and you let the motor run at low rpm. LiFePo absorb a lot more than traditional batteries which creates heat at the alternator. At low rpm a weaker alternator may become too hot. You mention that you have a D2-40 motor and this motor should already have a 115A alternator. Certainly I am happy to see comments but to date I cannot report any problems. A friend of mire replaced similar traditional batteries with 3 100 Ah LiFePo batteries and did not change anything. He is considering to replace the 230V charger with a more powerful device to reduce the period of time required to load the batteries - maybe it is worth mentioning that he uses 12V current also for TV, espresso machine etc. hence his consumption is a lot larger than ours. 

[Scorcher IV]

Thanks for the responses I feel happier now, I have enough space to get both 180AH in side by side. Unfortunately the costs of the LifePo means it will be Varta replacements.

[SYJetzt]

I suggest not to compare the price of a Lifepo battery with a Varta LFD system. From the Varta (and from most  of Lead- based batteries) you will get 500 cycles at maximum, if you discharge your housebank to 50% ( so you have only 180Ah for your disposal, if you fit 2 180Ah batteries). A comparable Lifepo4 system has a capacity  of 2x100Ah, from which you will get far more than 2000 cycles if not deeper discharged as 80%. Not to mention far shorter charging time, less weight, no hassle with charging lead acid batteries to full state and far longer lifetime.

[symphony2]

Surely it depends on whether your pattern of usage justifies the cost. They are between 2 and 3 times the price of AGMs or lead acid and for many leisure users the latter are perfectly adequate in terms of life and capacity. If however your usage pattern, for example constant liveaboard relying heavily on your 12v system you may be able to justify the cost in relation to the additional benefits of increased cycles and faster recharging.

Really no different from any other consumer choice, you look at what is available and weigh up the pros and cons of each alternative in relation to your specific needs.

[Krumelur]

Is it safe to replace just the batteries without adjusting the charger? Wouldn't the LeFePos need a a BMS?
I witnessed my neighbours house burning down after a Lithium battery went on fire.

[SYJetzt]

Drop in LiFepo's come with a built in BMS (like battleborn or dragonfly), so the battery protects itself from being deep cyled or overcharged. You should check the charging characteristic of your charger, ie the charging voltage, which should not be higher than the rated voltage of the Lifepo's. Common Lifepo's have a charge voltage of 3,6V/cell x4 = 14,4Vs  which is pretty the common voltage for chargers like the Quick chargers fitted in my bavaria, if adjusted to Gel-Battery-Characteristic.
Attention should be paid to the alternator, like mentioned by Holger.
In my case i dropped the battery isolator diodes, connected the alternator directly to the starter battery (80Ah flooded lead acid) and fitted a B2B-Charger between the Starter battery and the House bank (Lifepo). B2B Charger will be started if Alternator is charging the starter battery (detected by D+ on alternator) and temperature of alternator is lower than 80°C (detected by thermo-Switch)
Under no circumstances charging devices like solar chargers or the above mentions B2B-charger should be cut off by the internal BMS of the lifepos because their charging circuits will be blown up! So the correct setting of the charging voltage isn't critical for the lifepo, but for the chargers.