This is part of a series of unbiased reviews on products that I have tried – and in some cases use long-term in my own motorhome. Some of the products you can find in my store and obviously I make money on their sale, but I only sell things that I would use myself and would genuinely recommend.
Please note these reviews are the IP and Copyright of Wildebus.com and should not be reproduced or linked to without permission.
Overview
Trickle Chargers work by being active when the Leisure Battery is being charged. I would not neccessarily call them ‘Chargers’ as such as they work by sending a small current to the Starter/Vehicle Battery and not a managed charge of a battery. There are a few different manufacturers of these devices, but the one I believe is the best is the AMT12-2 Battery Maintainer from Ablemail.
The AMT12-2 has a number of advantages over the other options. It has 8 pre-set programmes that can be chosen based on a combination of if you have a Smart or Conventional Alternator, a Lithium or Lead Leisure Battery and a normal or higher residual draw on the Starter Battery. This optimises the function of the Battery Maintainer – compared to the other maintainers that have no options whatsoever and have to attempt to satisfy all combinations in one, and to be frank, do not fully succeed.
All these various Battery Maintainers are super-easy to install, just needing access to a connection to the Starter Battery +ve, the Leisure Battery +ve and a common Ground/-ve and the AMT12-2 is no different, so is very much a “fit and forget” unit. The cabling doesn’t even need fusing on the AMT12-2 side as it has integral self-resettable fuse within the Maintainer Body.
Setting Options
The following table shows the 8 different preset settings available to select from if you want to change from the supplied default (or the setting you requested from the seller). Once set, this setting is used unless you change it, so very much a one-time thing to suit your setup, but also one that can be changed easily should changes be needed (maybe changing from Lead Acid to Lithium Leisure Batteries for example).
| Setting | Alternator Type | VB Threshold | LB Type | LB Threshold | VB Drain | Time On | Time Off |
|---|---|---|---|---|---|---|---|
| 1 | Standard | >12.8V | Lead Acid | >13.0V | Regular | 6 Sec | 15 Sec |
| 2 | Standard | >12.8V | Lithium | >13.5V | Regular | 6 Sec | 15 Sec |
| 3 | Smart | >12.4V | Lithium | >13.5V | Regular | 6 Sec | 15 Sec |
| 4 | Smart | >12.4V | Lead Acid | >13.0V | Regular | 6 Sec | 15 Sec |
| 5 | Standard | >12.8V | Lead Acid | >13.0V | High | 10 Sec | 15 Sec |
| 6 | Standard | >12.8V | Lithium | >13.5V | High | 10 Sec | 15 Sec |
| 7 | Smart | >12.4V | Lithium | >13.5V | High | 10 Sec | 15 Sec |
| 8 | Smart | >12.4V | Lead Acid | >13.0V | High | 10 Sec | 15 Sec |
| 9 (Override) | N/A | N/A | N/A | N/A | N/A | 9 Sec | 1 Sec |
When the parameters for the setting selected are met, then a pulse of upto 3A is sent in 3 second bursts, with the LED lighting green whilst active. So for example, if setting 4 is the selected option, the AMT12-2 will be active for 6 seconds as long as the Vehicle Battery is not above 12.8V and the Leisure Battery is greater than 13.0V.
As mentioned, Trickle Chargers/Battery Maintainers are meant to work by being active when the Leisure Battery is being charged. That is the default MO and if there is not enough charging happening, the Trickle Chargers can effectively stop trickling. Common over wintertime especially. So being able to force a Trickle Charger to be active when it normally wouldn’t be can be very useful, especially when away in storage say.
And this is another area where the AMT12-2 wins over the alternatives – it can be used essentially as a ninth setting that is accessed by using an override feature. When in override mode, the Battery Maintainer does not rely on the Leisure Battery being on charge to be active, it will be activated on a 9 seconds on/1 second off duty cycle. This is the “9th” setting in the table above which is accessed on demand by applying a 12V signal on a tab on the AMT12-2.
Conclusion
This level of parameter selection to suit the various possible multiple different configuations in a “fit and forget” installation, plus an override ability when occasion would benefit from it is pretty unheard in the world of Starter Battery Trickle Chargers/Battery Maintainers and makes the AMT12-2 the only device I would recommend and would fit for this purpose.
Now that would normally be the end of this review, and for most people that covers all you need to know ….
We have covered the main functionality of the AMT12-2 in this review, but there are more features within it and that can be employed to make even more flexible!
Critical Battery Maintenance
As well as having the usual Battery Maintainer features, activating when the Leisure Battery is getting a charge – but tuned as explained so it is optimised for Lead or Lithium, and not sending a charge pulse if the Starter is already at a healthy level, the AMT12-2 has built-in a ‘Battery Guard’ programme that will attempt to look after the Starter Battery regardless if it starts going below a certain voltage.
If the Starter Battery drops below 12.1V, the AMT-12 will activate regardless of the Leisure Battery receiving a charge itself, as long as the Leisure Battery is at least either 0.3V in the case of a Lead Acid battery or at least 1.0V higher in the case of a Lithium battery. This will use potentially spare capacity in the Leisure Battery system in order to try and save the Starter Battery from dropping down to a potentially dangerous voltage (in terms of Battery servicability).
However this will only continue until the Starter Battery drops below 11.5V, at which time the Maintainer will stop sending a charge current pulse. This is to prevent the Leisure Battery itself getting dangerously low whilst attempting to save a possibly failing Starter Battery.
This built-in Critical Battery Management in the AMT12-2 allows it to do its best with the Battery Resources available to keep both Starter and Leisure Batteries as healthy as possible.
(It should be noted that the Override function does ignore all voltage thresholds so this feature is bypassed if using the Override)
Remote Override of Battery Maintainer
I mentioned earlier about the ability to override the selected setting of the AMT12-2 with an override. This I have found a very useful feature and have fitted a physical switch in my own Motorhome, connected to Switch 2 on the AMT12-2, in order to carry out this function if it is being unused for a time in order to keep the Starter Battery topped up in Winter, when adequate Leisure Battery charging from Solar is hard to find.
However, a physical switch is not the only way to do this. If you connect Switch 2 up via a programmable relay such as a Victron BMV Battery Monitor you can control the override remotely via an App and ‘toggle’ the relay setting. If you have a BMV-712 Monitor, you can even set the relay to go on and off (so turning the override on and off) based on the Starter Battery voltage).
And the ultimate in control … if you have a Victron setup with Victron Venus OS device such as a Cerbo GX unit and have remote monitoring, you could set the AMT Override on and off (via the BMV or Cerbo GX Relays) from the comfort of your own own home! Ideal if you have to leave your Motorhome in storage but want to be able to keep everything in top-top shape.
I have connected in parallel both a physical Override switch AND a connection to a Victron BMV-700 that connects to a Cerbo GX. In this way I have both easy ‘local’ control via the switch and world-wide remote control to look after my Starter Battery in the optimum manner!
Fine-Tuning of the Settings and Monitoring
We know the AMT12-2 has 8 user-selectable pre-sets to choose from; We know it has an Override Function,; And we know it has a Critical Battery Maintenance feature. But you can – if you want to – go even futher with in by creating your own profiles and settings!
If you team up the AMT12-2 Battery Maintainer with the Ablemail ABB-07 Bluetooth Module it opens up the possibilities of accessing the internal thresholds and parameters to your very own preferences. If you had an especially high parasitic load on the Starter Battery, you could change the ON/OFF duty cycle balance for example, or raise the Battery Guard threshold if you want to stop the Starter Battery going very low (a popular consideration for those with FIAT Ducatos and its siblings, Benny Boxer and Rodney Relay, and worried about the Airbag ECUs).
As well as modifying the setup (and a word of note: it IS possible to end up with a very bad setup as you are allowed to set virtually anything – but you can always use a factory pre-load or just go through the setting selection process to get back to a known position), you can also monitor the function of the AMT and also use the Smartphone App to report on the voltages of both the Starter and Leisure Batteries. Below are a couple of screenshots ….
AMT12-2 Settings Page – Some changes made from the usual!
You can configure just about any setting you like via the App.
Battery Manager view – Reporting status of device plus both Battery voltages. On the lastest AMT12-2s, you can even turn the override on and off via the App!
NOTE: While the “TURN OVERRIDE” Button will appear in the app, it should be noted that it will only have an effect on later AMT12-2 units shipped from around the start of 2024.
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