I’ve read the comments on the Hackaday.com article : https://hackaday.com/2025/12/02/lora-repeater-lasts-5-years-on-pvc-pipe-and-d-cells/.
Thanks for the feedback.

Most questions focus on two points

1. the real-world lifetime of alkaline D cells outdoors (You’re right: this is likely the main structural limitation of the current design), and

2. PCB protection in case a cell leaks.

I About alkaline D-cell leakage

Leakage can occur for two main reasons:

1. Deep discharge inside a series pack

At end of life, in any series string, the weakest cell will eventually be forced into reverse polarity if current keeps flowing.
This pushes the chemistry outside its intended operating region, causing:

• gas generation,

• internal overpressure,

• seal rupture,
  → leading to electrolyte leakage.

In my design, I continuously monitor pack voltage and put the device into a almost full shutdown if the voltage drops too low.
The whole point is to avoid that deep-discharge region which dramatically increases leakage risk.

2. Mechanical/assembly defects in cheap cells

This is the downside of the “500 Wh for €13” deal.
At that price point, you don’t get telecom-grade cells with industrial QC.
It’s a compromise.
As it stands, this is a structural limitation of the LoRaTube concept.

II Protecting the PCB/electronics in case of leakage

The mechanical design answers most concerns:

• the PCB is above,

• the battery pack is below,

• and the two volumes are physically separated by:

  • the 50 mm “coffee-cup” internal support, screwed into the 40 mm tube,

  • plus the piece that provides the positive terminal contact for the last cell.

The electronics compartment and the battery compartment are mechanically isolated.
If a cell leaks, the electrolyte cannot reach the PCB.
And if the cells become impossible to remove, the entire tube section can simply be discarded (a 2-meter PVC tube costs around €2).

III/ Toward a more resilient battery architecture

The comments are valid: if we’re aiming for extreme robustness, having the whole system fail because of one leaking cell or one failed cell is not ideal.

I’m considering a new architecture:

• instead of one long 18S1 string,

• use three parallel packs of 7 cells in series each → 7SP3 configuration.

This gives an input voltage between ~7 V and ~12 V depending on the state of charge.
The buck converter runs more efficiently and with lower losses in that range.

The obvious risk with parallel packs is cross-charging, which would destroy the weaker packs quickly.

Low-tech fix: Schottky diodes (passive ORing)

The simplest and most reliable solution is to place a Schottky diode in series with each 7-cell string:

• each 7S pack has its own diode,

• the three diodes meet at the input rail of the buck converter.

Expected behavior

Example:

• Pack A: 10.5 V

• Pack B: 10.2 V

• Pack C: 10.0 V

• Schottky drop ≈ 0.3 V

Effective voltages seen at the bus:

• A → ~10.2 V

• B → ~9.9 V

• C → ~9.7 V

Result:

• Only Pack A supplies current initially (it has the highest voltage).

• As it discharges, its voltage drops.

• Once it falls below Pack B (diode-included), Pack B automatically takes over.

• Then Pack C, etc.

This gives a very primitive form of current balancing, with zero active electronics.

Benefits

• The system keeps running even if one pack fails, or even two packs.

• Leakage or a broken contact in one 7-cell string no longer kills the entire node.

• You move from a single point of failure (18S1)
  to a system with graceful degradation (7S3 + diodes).

This matches the project philosophy:
long lifetime outdoors with simple, low-cost, repairable technology.

We could even consider 3, 4 or 5 parallel packs depending on:

• outdoor mechanical constraints,

• budget,

• desired level of redundancy,

• available space inside the tube.